Summary: 

With the Skeleton King risen once more, the Hyperforce has their hands full, alright. But when a report comes in of a lone shard of the Citadel of Bone landing on Earth and having been found by someone, Chiro and the monkeys head to Earth, specifically Japan, where they meet the Kitchen Ichinose Alliance in an attempt to hunt down that shard. However, they may end up getting more than they bargained for, with Chiro's past coming to light in the process...

Characters: 

Chiro is the leader of the Hyperforce, and seems to have a strange immunity to Skeleton King's advances despite his fears of being influenced by him. This is revealed to be due to the fact that he used to be Skeleton King's minion before he defected after he met Skellion, who left/presumably died, which means he's no longer susceptible to his manipulations. While upfront and a bit prone to goofing off, he knows when to get down to business and does his best as the leader to ensure no one else gets hurt. 

Ichinose Houtarou is Kamen Rider Gotchard, a rookie alchemist who fights alongside Chemies against Geryon and his forces. However, after the fight against Geryon in the Alchemist Academy, it's revealed that HE's the one who's picked up the shard, and it leads him to shed his "façade" as he attacks Chiro. While normally he's determined, a bit headstrong and optimistic, the influence of the Citadel of Bone shows a more vicious and creatively evil side of him, highlighting that even he's prone to having a dark side. 

Excerpt: 

The laugh was simple but man, did it send shivers down their spines as Geryon looked up, smiling all the while. "Oh, you had me GOOD. You really thought I was the one who had the shard to make these Malgams!"

Chiro bristled, even when ice began creeping into his mind, his gut feeling's screams suddenly more visceral... "What do you mean by that?!" 

Geryon smirked. "You had me, really. I never felt it, not even once, that you were the one. But now, it makes sense that my Malgams suddenly got so much stronger! Being in proximity with that shard gave them a boost! I must have it!"

"Proximity...?!" Rinne scowled. "You're not making sense."

"Let's just end him right here," Spanner said, his hands already moving to slide a Chemy card into his Valvarusher. 

"Yeah, he's talking nonsense, we'll figure it out later on," Sparks agreed, his magnets whirring up again.

But in that midst, Chiro suddenly felt really, really frozen, a realization hitting him. 

Geryon hadn't been looking at him, no, he had been looking...

His head swiveled over. Images filled his mind.

"Is it really that scary, Steamliner? I think we should ask Sabimaru-senpai to analyse it, so let's pick it up..."

And then another.

"Oh, come on, it's not that bad... :3 Hm, is this what using forbidden alchemy feels like? Man, it feels so good...!"

No... it couldn't be...

Black met blue, and Chiro felt his feet, his mouth move. "GUY-"

And then, he pounced, and boy, did he POUNCE. Chiro barely dodged the attack, even as all the heads swiveled over.

Geryon burst out laughing. Atropos felt a smirk curl up on her face. "As it turns out... The guardian eventually fell to the darkness too."

Minato was pale as everyone watched Houtarou get up.

Spanner felt his face drain of color.

"You're a joke."

He had proven him wrong, on the count of being stupid AND naïve...

Rinne gasped, unable to believe it. 

Renge shuddered.

Sabimaru suddenly understood how it was like to be on the opposite end.

Clotho felt a glee like no other, though. "Oh? Looks like the Kamen Rider brat also fell."

Chiro was frozen, his heart hammering against his chest.

How had he not seen it? All this time... the shard had been nearby all this time..!

Houtarou met eyes with Chiro, with a twisted smile that spoke of evil as his hands moved to outline a necklace he had been wearing underneath his shirt; a splinter, the very shard they had been seeking. "Ahh, so the cat's out of the bag now, huh?"

"Unicon...?!" Rinne's Chemy sounded stunned. 

"The light, the dark, and then the grey! Maybe that was what I was all this time," he cheerfully said. "But I'm sorry, I can't let anyone have this shard! Geryon, you have no regard for Chemy lives, so I think it's time you had a taste of your own medicine."

He held out his hand, and his alchemy ring went completely black as Geryon suddenly threw his head and screamed. No mirth could be felt. It was like his entire body was being burned from the inside. 

The satisfaction in the Dark Sisters' eyes died out as they watched their master eventually turn into ashes, and Kyoka paled while covering her mouth. 

"Alright, now that's done, maybe I'll start burning you three too!" Houtarou then turned his gaze on Atropos and Clotho, even when Minato stood in front of Lachesis to protect her. "Sensei, you really have turned if you're protecting her."

"Ichinose, you need to think this through," his former teacher said seriously. "That shard is affecting you immensely and-"

"So I can't use it, yet you can use the Dreadriver? Stealing all the friends I've made along the way? Seriously? That's a really weak argument, SENSEI. I admit my own naïveté, of course, but you're just being hypocritical here," he said while lazily fingering the shard.

"Houtarou, you have to stop this, please. That shard, it ruins you, messes with your head," Chiro tried to convince him. "Skeleton King is messing with you!"

He snorted. "He's messing with me? Sure, so everyone hasn't been messing with me from the start? I took a kendo stick to the back because Spanner didn't see me as worthy of the driver and then blamed me for the Dread issue with Sabimaru-senpai. In the end, I work hard with so many things against me. Everyone seems okay with using me for their own plots. Heck, I'm surprised Geryon didn't do that to me, and that it was an alien that actually pulled it off!"

"Spanner, you did WHAT?!" Kyoka actually stared at her student, who actually shrank a bit. "I told you to observe Fuga's daughter yet you choose to go after a newbie?!"

"It was a long time ago..." he murmured, although his tone showed he wasn't convincing himself either, and Kyoka looked horrified at the thought while Minato was beginning to really let the thought sink in. His student had been HIT ON THE BACK BY SPANNER. Oh, he was gonna-

"On that note, though! How have you been tracking that shard, Chiro? I'm curious, considering that you were the first to figure out I had it after Geryon's hint?" Houtarou suddenly asked, throwing his driver away while walking closer to him. 

Chiro took a step back. "I-I-"

"It's like you have an affinity to it! Heck, the shard itself was super eager to influence you, and yet you resisted it somehow! Actually, no! It seemed like you were immune to it!"

"Wait what? Antauri, why is Chiro immune to the Skeleton King's citadel?" Otto asked the robot monkey, who paused. Otto did raise a good question... "It could be the Power Primate..."

Chiro didn't address it, choosing to focus on saving his friend. "Houtarou, please... this isn't the way! Whatever you want to do, you can get to it without falling into Skeleton King's grasp!"

Houtarou then smiled at that.

Chiro felt his spine freeze over. No. No. He couldn't have figured it out...!

"Ah, are you saying that... because you want to avoid another YOU, Chiro?" He asked lightly. 

Silence.

Chiro's throat dried up. "The Citadel... it showed you..."

"Just like how it was clueing you in to where I was, it was clueing me in to who you were. And I have to say, Chiro, you really, really missed out," he said with a shrug. 

"C-Chiro, what is Houtarou saying?" Gibson looked at him, eyes wide in shock. 

Chiro looked away, unable to say it, but Houtarou laughed again, his clothes even changing to match the atmosphere into a simple black shirt and jeans as he said, "Oh, so you never told them? About your REAL past with Skeleton King?"

"I..."

"Well, let me tell them, then!" He said cheerfully. "Seriously, for a former SPY FOR SKELETON KING, you really don't act the part."

His world shattered there as the monkeys stared at him in shock, and Chiro felt tears already streaming down his cheeks, emotion overwhelming him.

No... no... this was... this was...

"Antauri, Gibson, Sparks, Nova, Otto, I... I'm so sorry..." he whispered, falling to his knees as he ripped the badge off his shirt, detransforming while shaking. 

"You... Treasure Boy, that was too much!" Renge snapped. 

"Too much? Oh, then you'll HATE what's coming next," he said with a sinister wink, a portal opening underneath him. "Until we see each other again, Hyperforce, and I sincerely hope you don't go against me again."