I felt like some music would help with these three chapters since they're so important. So here you go.

"Necrozma is heading towards the Alter of the Moone. He must be stopped, at all costs."

Lunala's chilling words rang through me. It was unnerving. We all looked at Necrozma, dashing off, to see if we could do anything about him, but briefly after, a new telepathic link opened up in my mind. I didn't create the link so I wasn't sure who it was at first, until I heard a familiarly deep voice, "I apologize, everyone. This is Arceus. I have an urgent message for all legends."

I noticed everyone stopping what they were doing indicating they got the message too, so I did the same. 

"By sending Solgaleo and Lunala to deal with Necrozma, I have made a grave mistake. He seems to have latched onto Solgaleo as a parasite, leeching off the light he provides. For now we will call this forme 'Dusk Mane' . I have sent two of my strongest deities to stop Dusk Mane, with Lunala assisting as well. The rest of you may also fight, or gather any information possible to take him down. Thank you for listening, and goodbye." 

Arceus then cut off communications, leaving us on our own to handle Dusk Mane.

Victini shouted, "Come on, Necrozma's getting away!" as we all followed him slowly catching up with Dusk Mane. The distant Alter was getting closer and closer as we were led to Vast Poni Canyon, where I originally encountered Necrozma. Soon we cornered Dusk Mane, who was readying a Power Gem when his attention was caught by two huge glowing spheres. 

They then took on distinct colors; one blue, the other pink, before the spheres exploded to reveal who Arceus had sent. It was Dialga and Palkia. Dialga did a double-take when he saw me, and kept staring at me. In response, I stared backed at him, with a hint of a weirded-out expression.

I could just barely hear Dialga muttering to himself with a deep voice, "Well... this is awkward." Necrozma took the distraction as an escape opportunity and bolted past all of us while we were focused on the time and space dragons. 

Palkia, who had a slightly lighter voice, told his brother, "Dialga, pay attention! I'm usually the distracted one, not you!" Palkia then teleported in front of Dusk Mane, startling him. There was some sort of rainbow aura surrounding Palkia and suddenly the area around Necrozma began to simultaneously ripple, bend, and shatter, and in the blink of an eye Dusk Mane was gone. He just vanished. Palkia, who seemed to be a bit tired from using such a powerful attack, eyed where Dusk Mane had once stood before finally breathing out a sigh of relief. 

Dialga soon flew up next to Palkia as Lunala approached them, saying, "Dialga, Palkia, it's nice to see you two again." 

"Same for us, Lunala," Dialga replied.

Speaking of which, Lunala then looked down at where Dusk Mane once stood, then asked Palkia, "What exactly did you do to Necrozma? He's completely gone." 

Palkia casually answered, "Oh, I simply used Spacial Rend at full power. I'm not even exactly sure where he teleported to. What I do know is that I've bought us some time for now." 

Soon I heard a voice shouting from behind us, "We're here, we're here!" Flying towards us was Mesprit, followed by Uxie and Azelf. From what I heard, they're actually part of the Mythic Branch, but they usually can't come because it meant risking capture by leaving their respective lakes. 

Jirachi came over to them and asked, "Mesprit, Uxie, Azelf? Came to help Dialga and Palkia?" 

Azelf replied, "Yeah, that's exactly why we're here, Jirachi. Though we're lucky enough that the two seem to have done their job already." Seeing them all here, besides Jirachi, who was leaving to do her own thing, reminded me of why I was here in the first place: the rage of Dialga that killed the first Celebi. I wanted answers, and I supposed the Lake Trio could provide me with some.

I flew up to the three, where Mesprit said, "Oh, hello, Celebi! Do you need something?"

I replied, "Yeah, I'd like to ask you three something. What exactly happened to Dialga the day the first Celebi died saving him?" 

Uxie turned to me with a look of concern and answered, "No one's sure what happened to Dialga that day. I do have a detailed account of what went on." 

"Alright, go on, I'm listening," I told her with intrigue.

Uxie continued, "Dialga had been acting... unusual that day. He stayed outside his home dimension, around Galar's wild area, even though he was weaker. He was silent. We got worried about him and went to see what was wrong. We couldn't believe what we saw. Dialga's eyes were a deep orange. He was enveloped in a shadowy aura. The Adamant Orb on his chest and various parts of his body glowed the same orange as his eyes.. His look was one of rage, of uncontrollable fury. And then... then-"

"He used Roar of Time on us," Mesprit interrupted. She seemed traumatized. 

I felt awful for them, telling them, "I'm so sorry. It must've been so unexpected."

Azelf commented with sorrow, "It was horrible. I couldn't believe that he would try to kill us like that. In a sense, I was right. Whoever was attacking us from behind those crazed, orange eyes was definitely not Dialga." 

Uxie paused and then went on, "None of us were hit, but we could feel the time distorting from just being near him. I can't say for sure what was going on in his head. He seemed possessed, almost. We fled then, and Dialga continued destroying everything around him, luckily away from civilization. Palkia soon grew concerned and then tried to stop him, but after a long, dragging, fight, Dialga was too powerful for even him. We thought there was nothing we could do. That it was all over."

"Then Celebi proposed a solution. The time distorting around him... it had a direct connection with his madness. She went to stop him. Dialga charged a Roar of Time upon seeing her, but she didn't care. She flew right in... and Dialga was cured. We came back to see him reversing time to undo the death and destruction he had caused. He was sincerely sorry for something out of his control, that what happened led to Celebi's inevitable, incurable death. And that's basically what happened." 

All four of us glanced at Dialga now, who was cheerily chatting with Palkia and Lunala showing no trace of the insanity that once plagued him. 

Looking at each other again, Mesprit said, "Please don't blame Dialga for putting you in this situation. It's not his fault." 

Reassuring her, I replied, "Don't worry, I won't hold it against him. In fact, I've grown to accept my new life now." Then I remembered something. "Hey, didn't something similar happen with Groudon?" I asked the lake trio.

Azelf replied, "Yeah, I think so. But that's a story for another... um, time..." 

I could just feel the power behind me. The lake trio were backing up a little. Looking back out of curiosity, I saw none other than Dialga staring down at me, again. I heard Azelf whisper to her sisters, behind my back, "We're just going to go now..." before quickly flying off. 

Dialga finally told me, "In case you're wondering, no, I'm not mad."

I still looked at him, wondering what he wanted, before he relented, sighing and then saying, "Look, I'm sorry that you're here. I wouldn't be surprised if everything was overwhelming to you for your first few days. I overheard your conversation with the spirits. It must have felt like a nightmare from Darkrai." 

Gathering my courage, I responded, "Like I said, I prefer my new life to my old one. Even then, none of this was your fault, Dialga." 

He grinned a little and replied, "Thanks for understanding. But, I need to ask something of you. Have you been traveling through time at all yet? Since I'm the keeper of said force, it's my job to be concerned about this. I don't recommend doing so, drastic consequences could result."

I was really worried, and frankly terrified. I didn't know what to say, because I did time travel in the Relic Castle. An impatient, "Well?" from Dialga broke my thoughts, making me realize I had spaced out a bit. 

I finally answered him, "Ummmm.... once?" 

He scowled, "Okay... that could be a problem. Where did you time travel, and how far back or forward did you go?" 

If Dialga wanted answers out of me, he was sure making it difficult. 

"I did it in the Relic C-Castle. I traveled 2,500 years back," I stammered.

He tilted his head back with worry, continuing, "What exactly did you do while you were there?" 

I knew I had to fess up, saying, "I only went in the Relic Castle because I got caught in a sandstorm and there was nowhere else to go. When it subsided the entrance was buried. My only clear way out was time travel. I didn't time travel for long, just enough for me to fly out of the Relic Castle." 

The Temporal pokemon then replied, "No it wasn't. You very well could've used Psychic to move the sand away." I felt stupid. How did I not think of that? He continued, "But, as said before, you hadn't even been in this form for a week at the time. You were in a bad situation, and thus you went with the most obvious solution."

I gulped in response. Dialga, finally noting my fear, said, "I told you, I'm not punishing you. You're still inexperienced in time travel and you really can't be blamed. But it's still necesary to give you a warning. You should only time travel if it's absolutely necesary. Even then, be very careful. Playing with time is no laughing matter. Even a slight alteration can change the course of history as we know it. You're lucky you didn't the first time around." 

I looked back and forth with unease, telling Dialga, "Okay, I think I get the message," with him replying, "I just needed to make sure. I'm not kidding about what I'm saying... just be careful, alright?" 

"Yeah, I'll be careful. I don't want to mess things up anymore than you do," I replied. 

The steel dragon replied, "No wonder Celebi chose you for her role. I think you'll do it perfectly." I smiled, while he went on, "Now then, there is another matter at hand here. You can come if you like." So I did.

We went over to Palkia and Lunala, who were both nervous. Lunala was worried about Solgaleo, while Palkia was panicking over the thought of Necrozma returning to his true form. 

The two saw me and Dialga approaching and Palkia said, "We've met before, haven't we? I can see Dialga got along with you well, Celebi." 

I decided to cut to the point and inquire, "It's nice to meet you, Palkia, and you too, Lunala. What's this about Necrozma's true form?" 

Lunala spoke up, "I can answer that question. Nobody knows Necrozma better than Solgaleo and I. Basically, Necrozma has already taken in Solgaleo's light and by going to the Alter of the Moone, he can then absorb my light and return to his original form. There's no doubt he wants revenge for the pain he suffered. He's incomprehensibly powerful in his true form. However, there's still something off."

Dialga, Palkia, and I were all waiting for Lunala to go on, and she did, "Even in his true form, Necrozma will still be feasting off my light and Solgaleo's as temporary sustenance. To return to his original power, of even greater proportions, he needs the Ultranecrozium Z." 

Palkia asked, "What in the Distortion World is Ultranecrozium Z? Is it like our orbs?" 

Lunala responded, "In a sense. It's said to be the first Z-crystal, rooted into Necrozma before he was stripped of the light that was later converted into every other Z-crystal. Despite that, the locals had found some early Z-crystals before that, a question even I don't know the answer to. Luckily, the Ultranecrozium Z itself has been lost to time, not even Necrozma knows of its wherabouts. But if he were to find it..."

"He would gain access to a special attack. 'Light that Burns the Sky'. If Necrozma used this attack, it would be more than enough to disintegrate all of Alola into nothing." Lunala seemed like she wanted to continued, but Palkia signaled her to stop. He seemed to be sensing something. 

Dialga asked, "Palkia, what's wrong?" 

"A disturbance... I'm noticing a disturbance in spacetime near the Alter of the Moone," Palkia replied.

I panicked and flew off, knowing what I needed to do. Soon I found the other mythics playing around, and I shouted, "Something's wrong at the Alter of the Moone! Everyone come quick!" 

Mew, who I hadn't talked to in a while, said, "What?! That's not good. I'll teleport us there!" We all got around her, and she created a pink wormhole that we all went through. 

We all marveled at the Alter of the Moone. It was gigantic. Floating up above were Palkia, Dialga and Lunala. Suspicion hanged in the arid air. Soon, a spacetime rift opened up at the base of the Alter. Dialga and Palkia were worried and used their powers to try and close it, but even with the boost of the Lake trio nearby it was no use. The rift grew and grew until Dusk Mane leaped out of it and immediately started desperately running up the stairway to the top. 

Everyone started attacking Dusk Mane in vain, who simply evaded most attacks.  Mew and I combined our Psychics to hit him extra hard, but Dusk Mane shook it off like nothing as the stairway was crumbling. Eventually he reached the top, where Lunala fired a last-ditch Moongeist Beam at Necrozma, but he dodged it and returned a Sunsteel Strike in response, hitting back Lunala to the stone wall behind her.

Soon, a huge, white hole opened up in the stone wall and started firing a huge, green beam at Necrozma. Lunala, caught right where the beam fired out of, screamed in horrible pain, her body glowing and glowing until the beam vaporized her completely and almost appeared like it was transferring her essence to Necrozma. All we could do was watch as Dusk Mane became enveloped in a huge ball of blinding, white light. It grew and grew and grew until it exploded, temporarily blinding us all. 

When our vision recovered, Solgaleo and Lunala were gone. Instead there was Necrozma. His body had morphed into a new, fragmented pattern, glowing golden. He then began rising, a body of pure light filling in the large gaps between segments, making him resemble a Dragon-type. 

The changes were finished as Necrozma returned to his true form. Everyone felt a level of fear unprecedented, not even when we visited Giratina. He raised his head to look out at the horizon. He wasn't crazed anymore, now much calmer. The proof of Necrozma's revitalized sanity came when he spoke out for the first time.

"3,000 years... after so long, the people of Alola will pay dearly for stealing the light that is now finally, rightfully mine."

AN: I was gonna upload this in a week from now, but I'm giving you guys an early present. But anyways, the Necrozma arc has begun! Please review if you'd like! Thanks for reading!