Chapter will be kinda shitty, but I gotta write while the ideas are flowing!! You understand right? if it turns out to be literal shit I'll take it down and re-write some parts.

(3rd person p.o.v)

Rin squinted as the blinding sunlight shown through the window and right into his eyes. He cursed under his breath blinking, trying to adjust to the brightness and the pain he felt in his eyes sockets. It was never this sunny in Gehenna, and it was even darker inside the palace. He would have to readjust to the scorching sunlight. He stretched, trying his best to shake off the drowsiness. Yes, it was not necessary for most demons to sleep, but he still did it anyways to regain his strength more quickly.
Rin felt this heavy weight on his chest that just would not leave, and he did not know the cause.
When he felt something move against him he looked down to see the green haired demon snuggled up against his side. His head resting on his chest, obviously being the cause of the pressure. He watched as he stirred awake rubbing his tired eyes.

"You do know that there are two beds in this room, right?" He smirked. He sat up, stretching his arms.

"Yeah, so? I'm not seeing your point." Rin chuckled and pushed him off him.

"Mephisto said we would start the investigation today, remember? We need to get up, now."

"5 more minute mom." Amsimon said snuggling more into the pillow.

"Get up!" He yanked him off the bed causing him to land on the floor with an 'oof!'

"That wasn't very nice." He puffed

"Who said I was nice?"

Amaimon crossed his arms at him and stuck out his tongue.

Rin chuckled. "You look horrible, you have major bed head."

"Be quiet. You have 24/7 bed head.

Rin scoffed and turned away, he then quickly fixed his hair situation mumbling under his breath.

"Let's just get ready leave ok?" With a snap of his fingers he was looking refreshed and was fully dressed in a different outfit. Amaimon did the same, his outfit looked like something he'd usually wear and stuck to the same colour scheme.

"We can ride on behemoth, it's also best to bring him with us since he can track almost anything." Rin nodded and proceeded to crawl out the window even though there was a fully functioning door right there.

*~*~*~*

Despite Yukio canceling all cram school classes, postponing the test and telling his students to stay inside their dorms, they somehow all ended up inside the large van with him on there way to the Vatican. They all insisted that they had learned a lot in those past years and that they could contribute in some way. Then along came Sir Pheles, and the students begged him to let them all join the mission. With a malicious grin he agreed to let the students come along. "But this mission is extremely dangerous, they could lose their lives!" Yukio exclaimed.

"If they're willing to go knowing the consequences then let them go."

"But they're practically children!"

"Aren't you the same age they are? Maybe a bit younger. That's an invalid argument.

The students cheered, they would be able to go on their first port ant exorcist mission since the Kyoto trip to exorcise the impure king.

Which lead them to where they were now, at the Vatican surrounded by Japan's best exorcists, discussing their plans on how to solve the situation.

~*~

Was it ever a good idea to make exorcists work alongside demons, let alone place demons with exorcists in the same room? Perhaps not, but it would certainly be one hell of a show.

Just about every exorcist of every level in Japan had gathered once they got the news that a powerful top ranked being had made there way into Assiah. All wanted to do there part to slay whatever the threat to them was.

Yukio stood with his students gathered around near him, they discussed amongst to themselves their theories of what the situation was.
All they were told was that it was serious, it involved a high level demon and peoples lives were a stake. Weather this was related to that phone call Yukio got in the middle of class about finding high traces of demonic energy in Japan, he did not know.
All he knew was that it would be a difficult and dangerous mission.

*~*~*~*~*

Soon enough Amaimon and Rin had arrived at the Vatican riding on behemoth. They were just going there to meet Mephisto since he said he would be there. They wanted nothing to do with the exorcists and definitely would not be working with them to solve the case.
There is no way that any human is qualified to do a demon king's job, and with the two of them on Assiah and all their brothers helping them out, they had it all under control already.
They entered the holy building, it wreaked of blessed salts and they could practically feel the anointed objects repelling them away. It was very uncomfortable to even be near the building. Rin had been in this building before but he never felt this invisible force that wanted to keep him away. He figured it must be because his demonic side had awakened.

The demons decided it would be best if behemoth didn't come in with them. Leaving the large beast outside the hopped off and headed towards the entrance.

When Rin and Amaimon entered the building, though it was quite difficult, they were shocked to see that it was completely filled to the brim with exorcists.

Their eyes widened. "Oh Mephisto, why?" Amaimon said.

"I told him not to get anybody involved! He said maybe three or four people would be joining, not three or four dozen!" He said pinching the bridge of his nose.

"Maybe even more than that."

He watched as the people chatted amongst themselves, loaded with weapons, not acknowledging their presence. "I should've known not to trust a single word that came out of that clowns mouth."

Over these years he had developed a hatred of being around humans, they were frustrating and stupid and smelly. He wondered how he was even able to live amongst them for so long. They wreaked of ignorance, must be nice, to be so clueless, as they say 'ignorance is bliss'. How do they go about their lives, so uninformed?

Rin thought that it was because humans don't live very long and they only live amongst other ignorant humans. They're not like demons who live forever and have so many years to become wise, to learn, to see how it truly is. But he couldn't blame them, he didn't become so wise until he reached his early 90s and humans are dead by then...if only they listened to their senior citizens, I'm sure they would learn a thing or two about society from them. Yet again, they might be ignorant too being that their humans. Maybe they should hire demons as tutors, they'd teach them a thing or two, and a thing or two out respect too. Disrespect a high class demon and they lash out.
The sight of an angry powerful demon is never pretty.

"Well, this isn't going to be fun. Stuck in a room full of exorcists who attack demons on sight." Amaimon said looking around.

"Yeah, let's just find Mephisto and get this over with."

*~*~*~*

As soon as the demon king of time noticed just about everyone had arrived. He cleared his throat.

"Well I'm glad to see that you were all able to make it here, your help is greatly appreciated." The two demon kings rolled their eyes at that.

"You said that there's a high level demon running through Assiah!" A lady called out.

"Well...those weren't my exact words but yes. There is a possibility that there is a high power levelled being that found its way into Assiah-"

"Well we need to start right now before any lives are put in danger! We can track their demonic energy with our new chants we've been working on." Another shouted out.

"If you'd just let me finish-"

"We'll split up into groups and start the search." Then immediately everyone disbanded and got into groups to start the search did the being that opened the portals.

"...mortals these days never listen. When when they start to get themselves killed because they don't know what they're up against they better not come crying to me." He muttered to himself.

~

"Alright students, we don't know what type of demon we're facing, so I suggest we all stay together. Shura will be joining us today." Yukio said to his students.

"Um Okumura-sensei, do they r-really not know wh-what type of demon we're after?" Konekomaru asked.

"If we don't know what we're even looking for, then how are we going to know it when we see it?" Izumo said crossing her arms.

"We'll know it when we see it." Said Bon.

"Yeah, but how?" She said with sass.

"Because it will be a powerful high level demon causing trouble!"

"There are lots of high level demons that could be causing trouble, how do we know that it's specifically what we're looking for?"

Bon grabbed a fist of his hair angrily shouting. This girl kept trying his patience. The two started arguing again for hundredth time that month. Yukio and Shura tried to break up the fight.

"Do you seriously have to do this here? In the Vatican, in front of all my superiors?" She said pulling Izumo off Bon. "How's this gonna look on us? You're our students! We're supposed to have you under control?"

"You're all practically young adults now, you're too old to be acting like bickering five years olds!!" Yukio tried to calm them down.

Shiemi watched worriedly as her friends argued.

'Why do they always have to fight.'

I hate seeing my friends upset with each other. Why can't we all just get along'

Shiemi thought to herself looking around when something caught her eye, or rather, someone.

~

Rin and Amaimon made their way through the crowds of people trying to find their second eldest brother without coming into too much contact the humans. Rin had a bone to pick with him. Finally he spotted the purple haired man dressed like a circus freak.

"Hey clown face!" Rin said storming towards Mephisto.

"Oh, Rin, I'm glad you actually decided to show up." He said with a grin.

"Oh can it Samael!" He used his real name, that his they knew he was being serious.

"I'd prefer it if you didn't use that name while we're here." He said with a dark tone.

"You said that you'd only bring three or four exorcists, not a whole flock!" Disregarding his tone.

"Well, there was a change of plans. I couldn't stop them all from randomly showing up. Word spreads fast you know." He said leaning forward with two hands on a cane that seemed to magically appear.

"I'm not working with all these people, I can tolerate just a few people as long as their not ignorant towards anything inhuman, but I am not willing to work with dozens of -of!-"

"These people are very educated in what they do, and I know that you don't like working with humans but what I ask is that you allow them to at least help us track down the source opening all the portals."

"Do they know that we want the culprit alive?! No, and even if they did they'd just kill it on sight! Getting all these humans involve can put the lives of innocent supernatural creatures at risk! Do they even know that it might not even be a demon we're after? If it's not a demon what good are their weapons!? We want the one opening the portals alive and sent straight to Gahenna for questioning, not have it destroyed along with many other citizens who were unfortunate enough to get in an exorcists way. If I find that they have killed our kin I will not take this lightly!" Rin growled.

"Calm down younger brother." Mephisto said with a smirk.

"Calm down!" He seethed. Flames started to flicker on his body as he felt himself loosing control of his temper."You put the lives of my citizens that I'm responsible for at steak. I. Will. Not. Calm. Down." He clenched his fists. Amaimon didn't bother to stop Rin from losing his cool because he knew the words Rin spoke were true. They wanted the culprit alive and they didn't want to risk the lives of anyone in the process.

~

Shiemi watched as the very same people who she saw in the building yesterday walked up to her headmaster, seemingly very angry. They are argued with him as the headmaster seemed perfectly calm, smiling even. What was the demon doing there at the Vatican?? And what were they talking about?

She couldn't help but think that the blue haired demon looked so familiar, yet so new. She stared at him trying to remember where she'd seen him before. Suddenly, her eye caught onto something. The smallest blue flame that sparked on his shoulder. More seemed to sprout the angrier he got.

'Wait, blue flames?'

Suddenly it all clicked!

The blue hair, those facial expressions, the blue flames that flickered in his black princely clothing. Tears started to well in her eyes.

'No, it couldn't be...
He disappeared so long ago, it couldn't be him,
But it must be.
He looks so different, so much older.
I'm not sure if it's really him,
but my gut is telling me that it must be.'

"Rin...?" She said with the quietest voice. She covered her mouth as the tears flowed down her rosy cheeks.
"Rin!" She said a bit louder this time, catching the attention of her class mates. They all looked at her confused.
"Rin! Rin! Is it really you!" She said with tears down her eyes. She ran towards him crying. He looked at her when he heard her call his name. She knew it was him for sure now. She recognized his face. She stretched out her arms running towards him, and embraced him in a big hug.

"Rin you're back I'm so glad you're safe! I'm so so sorry! I was a horrible friend! I beg you to forgive me!" She sobbed in his chest.

Suddenly she was forcefully ripped off him.

"Get off me woman!" He yelled.

"Rin?" She looked up at him confused. He had a hostile expression, his forehead was creased and his eyes were such a vibrant blue they almost seemed to glow. You could practically feel the rage emitting off him. "Rin it's me, Shiemi..."

"I know not who you are! But I don't know what has gotten into you that you think you can launch yourself at me and attack me! Do you have any idea who or what I am? What I'm capable of?!" The other cram school students rushed over to Shiemi after hearing all the commotion.

"Shi! What happened? Why did you just run off like that-" Bon's eyes instantly widened. No, it couldn't be.

'Am I hallucinating?' Bon thought to himself.

' No way' - thought Shima

'I can't believe it. He's alive!' Izumo was stunned.

'I thought he was supposed to be gone for good! How is he back?' Konekomaru internally panicked.

"Okumura, is that you?" Rin scowled at Bon.

A bunch of strange humans come crowding him acting like dumbstruck fools? What is this?!

Yukio pushed past the crowds towards his students.

"What's going on here-" his eyes caught onto his twin brother who was supposed to be missing. Saying he was surprised was a major understatement. He had a lot of mixed feelings about seeing him here. He wasn't too sure if he was happy to see him alive and well, or infuriated that he had returned. Especially how he had returned.
Rin was his brother, no matter what you care about your kin at least a little bit. But Rin had also caused him a lot of problems. He was a great burden on him and while he was gone that burden was lifted.
But with the mass panick, the worry in his students and Shura's voices. And not to mention Izumo talked non stop about how they treated Rin. He had begun to feel a twinge of guilt.

Rin's eyes locked onto Yukio, glasses, moles, stupid hair, he immediately recognized him as his twin brother, though they definitely looked nothing alike now.

"Rin." He said through a clenched jaw

"So, we meet again brother, such a displeasure to see you." You could cut the tension in the room with a chainsaw. Yukio instantly took note of the change in Rin's appearance.
The pointier ears, the deathly pale skin, the bright blue hair, the unnatural colour of his irises.
All feelings of sorrow and guilt evaporated when he saw Rin's new form. Rin was no longer his brother, he was traitor.
"What on Assiah have you done with yourself? You look like complete monster." Yukio said with an angry look. Rin glared right back at him, Amaimon also glared at the humans standing even closer to Rin, in case the humans tried anything. Those where the very people that put his little brother in such a depressed state. Who hurt him to the point he considered taking his own life.
The cram school students looked at Rin shocked, they weren't used to seeing the usually happy-go-lucky boy act so hostile towards them. The defensive stance like he had his guard up, and the angry stone cold glare. Yukio's glare became just as hostile and he too got into a defensive stance.
"Oh I see. When you disappeared, you ran off to join the demons." He spat. "You abandoned your friends and family for them."

"They are my family." Rin defended which only seemed to fuel Yukio's rage.

"How could you? What happened to wanting to become an exorcist? Wanting to defeat Satan? You betrayed Father, you let him die in vain. You never liked him, you are always fighting. You probably sided with Satan just in spite of him." Rin balled his fists so tight that his knuckles became white.

"You and I both know that isn't true. I did care for the old man. He raised us from infantry. But he didn't even bother to tell me the truth about who I really was. He stole us from our real father Yukio. He was right there when we were born and the old man just took us away."

"That's disgusting. How could you even think like that for a second! He saved us from that beast and taught us everything we know!"

"He spoon fed us lies!"

"Is that what the demons told you. What they brainwashed you to beleive? They're the ones who obviously abducted you. And convinced you yo turn against us. But weather I like it or not we are still blood related. If you deside now to turn back and admit you're wrong. Then I guess we will welcome you back. And purge your mind of that nonsense they filled it with."

"Welcome me back? I was never welcomed in the first place so why would I be welcomed back? And what you said was all wrong. I chose to leave Assiah. It was no place for me anyways."

"So you willingly betreyed everyone!!"

"You don't get it, do you? You never will." Rin took deep breaths, he didn't want to fight with him, he was a king, he was better than this. He had years of counselling from Azazel to control his rage, he wasn't about to let his words get to him. Inhale, and exhale.

It had been so long, and Yukio still didn't get it. Get why Rin had left this place he used to call home. Why he abandoned his fake friends and family for the real deal.

"Do you want me to kill him, brother?" Amaimon asked putting a hand in his shoulder.

"That will not be necessary Amai-nii, remember what Samael said, we're not allowed to kill anyone while we're here."

"How could you refer to that monster as your brother! How could you act so friendly with him after he tried to kill you and all your friends! He ruined your life Rin. He's a demon king, he's dangerous and has killed thousands of people! He has ended thousands of innocent lives and your going to treat that demon scum like family?!" Yukio yelled. That was the final straw for Rin.

"HOW MANY INNOCENT LIVES HAVE YOU TAKEN WITH THAT GUN OF YOURS!! HOW DARE YOU CALL HIM MONSTER WHEN YOU YOURSELF ARE EVERY BIT AS EVIL IF NOT WORSE!!" His echoey voice boomed. "You ruined my life Yukio! Not HIM!!"

Yukio charged at Rin yelling in rage. Within seconds Rin had lifted Yukio off the ground by the collar of his shirt as if he were light as air. Rin effortlessly threw Yukio across the room, his back hitting the wall with such a force, enough to cause a crack in the wall. He fell to the floor groaning in pain, slowly he propped himself up on his hands and knees. Yukio wiped the blood running from his mouth and stood back up glaring at Rin. The cram school students ran to his aid.

"Yuki! Yuki are you ok?!" Shiemi asked frantically helping him balance himself. His eyes locked on his target and again he charged at Rin pulling out his gun. The others called out to him.

"Don't get in my way! He's not Rin any more, he's released his powers from the sword. Now he's just a no good demon." He aimed his gun at Rin's head pulling the trigger. Almost at light speed Rin had summoned up a demons sword, blocking him from the shot, repelling the bullet. The blade had been so sharp and strong, and placed ever so precisely that it had sliced the bullet in two.

Soon enough every exorcist was on him, saying that he had lost control and was now attacking. They were ready to execute the demon, they had found the escaped son of Satan that had disappeared years ago and they didn't intend to let him go. Multiple people shot mercilessly at the two demons but Rin had easily summoned two swords and was able to block every shot.

Shura was amazed at his abilities, the last time she saw him he was barely able to light a candle with his powers or control when he burst into his blue flames. He could hardly use his swords properly, he failed simulators and his attacks were really sloppy. But within the two years he had been gone he was suddenly able to block bullets with a blade?? Perhaps only one or two little flames had sprouted on his body, he wasn't totally engulfed in them. He was moving at such speeds, that she had never seen done by anyone. She was so sure back then that he was so weak and had no control over his own power that he'd be no real threat to anyone, but now? Now he was the ultimate weapon! He could easily defeat anyone and possibly even kill Satan.
[A/N: Bitch please!! No one's gonna kill Satan 😂😂]

People were running out of ammo and Rin showed no signs of slowing down. Amaimon had helped too by fighting off other people with his powers, it was fairly easy. He transformed into a more demonic form. He had horns, had grown a couple feet taller, and had a tail like that of an alligator making him more horrifying. The two demon kings fought so well together. That came from years of sparring together and engaging in fights together. They each fought off the exorcists, defending both themselves and each other.
People seemed shocked by their capabilities and it had been clear that demon kings were able to do so much more than they had thought. None of their chants or holy verses did anything.

Amaimon took on two guys while
Rin had been busy fighting off three exorcists at once, and was not aware at the one approaching him from behind. With a loud cry the exorcist stabbed Rin in the back with all his strength. He ripped out the holy blade, it drenched with thick dark blood. Rin had paused for a moment after being stabbed. He was sure that he was victorious since the demon king seemed immobile. The blade was blessed by multiple priests and was to easily kill any demon it was used against. It was sharp and strong and able to cut through many strong materials. It was to completely stop the demon from being able to heal the wound leaving it to quickly bleed out. The exorcist watched in absolute horror as the wound quickly stitched itself up. 'How could it be? The blade is blessed!' The demon king whipped his head around, teeth razor sharp, obviously enraged about being stabbed. Rin took his sword and with one swipe slit the man's throat. 'Oh well, so much for not killing anybody, Samael is going to be very upset with me. Though he had it coming.'

"That's no fair, I thought you said no killing?" Amaimon asked.

"This one had it coming. Let's get out of here, yeah?" The two looked around at everyone running around like chickens with their heads cut off. Screaming at the top of their lungs, many were bloodied and beaten up, or wounded by the bullets being rapidly deflected. "How about we go get Assisah ice cream?" Rin asked.

"Yay! First a tour of the city while riding on behemoth, then beating up humans, now ice cream? This really is a great day." Rin smiled.

"Come on." Rin wrapped his arms around Amaimon, sprouted huge wings made of fire, and then flew away. Instead of taking the door they crashed right through the ceiling and took off into the sky while Amaimon screamed "Whoo hoo! Ice creeeeeeeeaaam!!"

They all had wide eyes in disbelief at the sight.

"Well, wasn't that quite a show?" Mephisto said sitting in the corner eating popcorn.

"Is this a game to you?! Look at him eating popcorn while this all went down." Bon said frustrated, they had took cover behind seats while the bullets flew everywhere.

"What the hell was that?" Shima asked getting up dusting himself. They looked around, this place was a dump, bloodied bodies on the ground, people groaning in pain, 3 quarters of the people had fled.

"Did you see how Rin looked. He was so angry and scary." Shiemi shuttered.

"I-I know." Konekomaru was shaking in fear.

"Is everyone alright?" Yukio asked.

"No, have you looked around?" Izumo said gesturing at all the injured people.

"Never mind that, have you noticed how much more powerful he has gotten?" Shura said putting away her weapons.

"Of course he's gotten stronger, he's had 200 years to train." Mephisto said matter of factly.

"2 hundred - what?!" Shima asked.

"But Rin was only gone for 2 years headmaster." Shiemi said confused.

"Time works differently in Gahenna, it has been only 2 years for us, but for Rin it has been 200 years."

"Is that why he didn't remember us?" Shiemi asked looking down sadly.

"Well, he hasn't seen us for 2 centuries, that's a lot of time of course he forgot." Bon said dusting rubble of his pants.

"What are we going to do now? Are we going to look for Rin now that he's back on Assiah? We need to apologize to him." Shiemi said. "He's probably just really upset."

"It's no use. He's gone full demon now, there's no reasoning with him." Yukio said.

"He's a demon, not a savage, I'm sure he's capable of being reasoned with. He didn't seem totally barbaric and insane when I saw him, just pissed which has the right to be after the way you ran your mouth." Yukio glared at Izumo.

"Now your siding with the demons too? Don't let them fool you Izumo, demons are good at persuasion, look at how they persuaded Rin to betray his kind."

"Last time I checked we're the ones who persuaded Rin into joining them. He wouldn't have left if we weren't such ass-"

"That's enough Izumo. You're not making anything better when you talk like that." Bon warned.

"I think you guys just can't handle the truth."

"We should all forget about him, he's a lost cause now." Yukio said.

"I-I agree with sensei." Konekomaru said. "We should leave him alon-"

"So he gains a few new powers and now he's a lost cause? Have you forgotten, he's your own brother!"

"Oh, I'd say he has gained more than just a few new powers." Mephisto reappeared next yo the group.

"What's that supposed to mean demon, and I want a straight answer now!" Yukio demanded.

"When Rin went to Gahenna he had fully released his powers and had them amplified-"

"We can tell."

"Let me finish, you are the one who demands answers. While he was down there he was also made into a demon king.-"

"A WHAT?!" Yukio yelled.

"They turned him into a demon king!?" Bon exclaimed.

"You act as though it was against his will. He allowed Satan to turn him into one."

"Satan- he's sided with Satan! Wasn't he all determined to kill Satan for murdering his old man and other people?! He was so determined to defeat him and now you're telling me he willingly handed himself over to him!"

"How does one even go about becoming a demon king?" Shima wondered to himself.

"It makes no sense?" Bon ranted. "How could he just-" He was both infuriated and confused. How could one go from being totally against Satan, has a set mission to become an exorcist and defeat him for revenge. Then suddenly become all buddy-buddy with the Demon God?

"So there's 9 demon kings now? Man, it's gotta be cool to be a king! What's Rin the king of?" He said curiously.

"Good question. He's the king of Darkness."

"So what, he controls the dark? Or is it dark as in evil, like, he controls evil things."

"Yes!" Mephisto answered.

"Yes to which one?!"

"Exactly!" Mephisto beamed.

"I'm so confused." Shima continued to ask more questions about Rin while Bon ranted about the whole situation infuriated and perplexed.

"How could he just- side with the demons! The enemy! They're evil! And manipulative and dangerous!" Bon went on.

"If you have so many questions about Rin, then ask him yourself. Though I'm not sure if he'd really want to see you. Or remember you at all for that matter."

"What do you mean we can ask him? He took off into the sky." Shima said confused.

"He's staying in the old boys dorm for the time being while we figure out the case-"

"Wait! Two demon kings are staying in our school!?" Miwa asked panicking.

"-Well I ought to get going, ta-ta. Eins, zwei, drei!" And with that he disappeared in a puff of purple smoke leaving the dumbfounded exorcists to comprehend what just happened with their puny minds.

Sorry that the transitions were literal shit, but wanted to get in every bodies perspective!

Sorry for any typos. Hope I didn't disappoint.