Rin's relief on returning to Gehenna was short-lived. He was happy he, and Satan hadn't hurt anyone. But he felt disgusted with himself for leaving in the manner he felt forced to, with Satan inside his body. He wasn't sure what was worse, his family seeing him struggle against his inner demon trying to force its way out or letting them see him succumb to Satan himself. Neither option was his first choice but as far as he could see they were the only ones he had at that present moment. Opting for the latter as it got him quickly back to the safety of Gehenna.

The painful throbbing in his head had subsided thanks to Satan quelling its anger in his control, but Rin could still hear the vague screaming in the back of his mind. But now he was faced with another problem. The one he had really wanted to avoid at all costs; the one that threatened everything he was. Facing his demon half.

Satan was adamant it had to be now, no more choices, no more delaying the inevitable. He'd made it clear - either join with his inner demon or Satan would take Rin's body as his own – and use it to kill Father Fujimoto. He wasn't sure if he was serious or using it as a way to motivate Rin to get a move on, Rin didn't want to risk it either. Regardless of everything that had happened, Father Fujimoto was still his dad.

Rin sat cross-legged on the cold floor of the throne room, where he'd woken up after Satan's possession moments before. His reluctance to this whole thing was obvious. He liked feeling whole again, but he didn't want this to change who he was. He just wanted the pain in his head to stop.

Satan circled around Rin, looking deep in thought. He finally stopped behind him putting a clawed hand on his shoulder. Rin flinched and felt the desire to shove it off, not wanting to be touched by the demon. Satan seemed to sense this and grasp tighter.

"Summon your flames." He ordered.

Rin did as he was told, the flames were weak and lightly danced around his form. Satan let out a disappointed huff.

"Put more into them, don't hold back."

He managed to push them a bit more, which cause the voice in his head to grow louder. He stopped pushing when the pain returned.

"More!" Satan tightened his grip again, digging claws into Rin's shoulder.

"I can't – It hurts" Rin gripped hold of his head. His flames dying slightly. Satan wasn't going to allow him to shy away from this, summoning his own flames he surrounded Rin with them, pushing them into his being – fuelling Rin's own flame to grow bigger. Rin's eye snapped open as the pain came back full force in his head, he screamed in agony as he rolled around the floor gripping his head. He'd never felt the pain this bad before, it was unbearable, his head felt like it was splitting open in all directions. Like it was being torn apart from the inside out.

Satan paid no attention to the screams and poured more power into him. He spared a thought for whether his renewed body would actually handle this, he'd already combusted once but he was tired of Rin suppressing this power; suppressing his rage. If he could survive this merge and his full power, he would be worthy of the title the Son of Satan; the Prince of Gehenna.

His throat felt raw, his head was splitting and his body ached all over. Rin finally blacked out, his body collapsing to the ground.

When he opened his eyes there was nothing but darkness, an endless sea of black. He sat up squinting to try and see something; anything. But it was no use, the darkness was too thick. After a few moments passed something formed in front of Rin, a dim light resonating from it. Two blue orbs stared back at him; a mirror had appeared.

He looked into the mirror to see himself, he looked human again. His hair was black, fangs gone and ears rounded. He felt around his lower back to find his tail had disappeared again. He was dreaming, he must be, just like before. He looked around but there was no Yukio, no Monastery; only darkness. Turning back to his reflection, it started to morph in front of his eyes. The reflection sneered at him, white hair, fangs and pointed ears. His other-self.

Rin glared back into the twisted flames of his other half's eyes. The demon stepped forward and out of the mirror, now stood in front of Rin who was still sat on the floor; his glare had morphed into fear. As the demon walked forward with a hungry look in his eye Rin scooted back until he hit something. Looking up he met more twisted eyes, the eyes of Satan.

"Welcome to the core of your mind." Satan finally said, smug grin evident on his face. Rin wanted to punch him. His demon-self chuckled.

"The core…of my mind?" Rin questioned.

He was suddenly face to face with his other self, far too close for Rin's comfort and staring into a hungry grin with far too many sharp teeth for his liking. He spoke with Rin's own voice, but it seemed more animalistic than his own, there was a low growl to his voice that made Rin shiver.

"The place I have been locked away for 15 years, waiting for release…" He growled. "I am created of all your rage and lust that you had denied yourself and pushed deep down. Just so you could be a worthless human that never fit in. I have been watching from the side-lines for 15 years, but now it's my turn to play—" He quickly pinned Rin down and gripped his neck, flames growing around his body he began choking Rin.

Satan quickly stepped in forcing the demon off of his human half. As if asserting authority Satan growled. The demon didn't push back, just glared at his father before turning his attention back to his human half. Rin coughed as he sat back up. Rubbing his neck, he scooted himself closer to Satan.

"I already warned you not to kill him" Satan growled at the demon.

"Why are you so adamant the human part lives when you want him to be more like a demon. If you'd let me get rid of him, you would have the demon son you wanted and a faithful servant to help you claim Assiah."

"You were born as one, you should return to one. Regardless of his humanity, your personalities will merge. You will still get your freedom."

Rin sat confused at the civilised conversation going on in his apparent mind, between the two demons. The Demon Rin looked lost in thought, staring at his human half with a wavering look on his face.

"And you actually agreed to this? Giving up your humanity to merge with me? Heh." He laughed to himself.

"I'm not being given a choice. I don't want to give up anything, but I want the pain to stop. I want the fight over my body to stop, so people don't get hurt if you suddenly escaped." Rin looked the Demon in the eyes.

"Tch, so self-sacrificing aren't you. Do you really think us merging again will stop that? You have no idea what we were like in the beginning?"

"What do you mean? You do?!" Rin looked at him confused.

"When we were still as one before they sealed our heart. My memories are vague…but I remember bits. There was fire and death and screams of terror - and we were the cause of it." He paused for a moment as his words started to sink in. After thinking about it himself now, it sounded like a good idea. "Ya know what? Maybe a merge would be fun…"

Rin faltered at that; a memory of him as an infant changed his mind, just like that? He was getting outnumbered on this merger, even his Demon half wanted it now…

"You never know, it could be different! We were only an infant back then, you're more mature now though, right?" He chuckled again; Rin grimaced.

Satan observed in approving silence, before looking into the distance to see something in the darkness. Could that be…? No surely not. How did he get here? Interesting. He might have to go and introduce himself properly. Then again was it a good idea to leave these two alone? They seemed to be keeping in civil for the moment. In the end, Satan decided to go and question the visitor.

"I will be back, try not to kill each other in my absence." With that Satan disappeared in a flourish of blue flame. They both looked in confusion. Turning back to each other Demon Rin had a glint of mischief in his eye.

"Let's play." He said with a big toothy grin.

"What?!"

"Play. Ya know, fight me! In our mind, we're more or less evenly matched." He leant forward with a look of excitement.

Rin wasn't sure "What's the catch…?"

The resulting grin on Demon Rin's face scared him. He wanted to run.

"If you win, we don't merge, and I will quiet down. You retain your humanity and still have all your power without me taking over."

"I don't buy that; you've been trying to get out for so long to give me that option. What's to stop you going back on it later?"

"I'm am a demon; we are bound by our deals." He shrugged, crossing his arms with a smug look.

"But what's the other half of the deal, what if you win—?"

The demon clapped his hands together; Rin jumped. "Ah! If you lose the fight against your demon urges." He gave Rin a wide toothy grin, Rin swallowed a lump.

"What do you mean…lose to my demon urges?"

"Where would the fun be if I told you that!" He pushed his hand further towards Rin's face as if waving it around in front of him would get him to shake it faster.

"And…then?" Rin said, pushing the hand to the side, much to the annoyance of the demon.

"And then we merge, like Father originally planned. If your humanity takes a hit and you are more demon than human, that will be the consequence. If not then you still win." He moved his hand back in front of him.

Rin stared at the hand in front of him still hesitant to shake it. "I'm confused. Do you actually want to merge now? What happened to taking control and being free to burn everything…" Rin was surprised and worried. Why would his demon half suddenly change his mind and want to merge, giving up his main chance at control?

"Fighting you for control is getting tiresome, for both of us." The demon turned serious, looking Rin in the eyes; crossing his arms.

"Human egos are stronger than demon egos. The only reason you're having trouble is because of what happened with those humans." Rin could've sworn he growled out that last part. "Even if I gained control, you'd fight me; I'd fight you back. Unless I killed you here and now but Father won't be so forgiving for that." He huffed in frustration, claws scratching on his arms.

"We'd just be wasting endless energy trying to suppress each other. So as much as I despise the idea; Father is right. Merging together will fix our issues. You'd no longer suffer the pain of me fighting you, and I would no longer be stuck in here." He once again held out his hand, to shake on the deal he'd proposed.

Rin sighed ignoring the demon's hand yet again. The demon's eye twitched.

"So, you've just been stuck in here, watching for 15 years?"

The demon nodded. "There were a few times, I managed to break free. I'm sure you remember the few times you've got carried away and hurt people."

Rin grimaced but nodded back in response.

"But you were human, there wasn't a lot I could do trapped behind the seal besides lash out. Then that damn priest managed to enforce your human will and I was suppressed back into the darkness again. There will be no more of that once we're merged." He growled with visible excitement.

"You sound so sure that you'll win." Rin looked at him with a serious look. He wasn't planning on losing his humanity to this demon. He was going to win, he wanted this thing to go away and leave him alone. Satan could shove his merger up his ass.

"Does that mean we have a deal?" The demon grinned hungrily as Rin took his outstretched hand.

Yukio opened his eyes to darkness, he felt around before realising his glasses were still on his face. Had he fallen asleep with them on again? He remembered falling asleep in Rin's bed after briefly talking with Father Fujimoto but this didn't look like his and Rin's room. There was no light filtering in from outside it was just pure darkness. Where was he?

After a while a dim light appeared in the distance, he could make out a figure stood in front of it, somewhat illuminated by the light. He soon recognised the figure as Rin, but he looked human again. Did they change him back? Was he in Gehenna? How did he get here? Too many questions forming in his head at that moment. He tried shouting to his brother, trying to get his attention. But Rin couldn't hear him, he stood up and tried to walk towards him but something in front of him prevented him from getting any closer. He banged on the invisible wall, hoping it would make some sound to make Rin turn around. Would he even see him?

Rin was looking at a reflection of himself, just realising himself he was human again before his reflection turned into that of a demon and walked out of the mirror in front of him. Yukio banged even harder, but it was no use. Another demon appeared behind Rin, older with long white hair, blue flamed horns on his head and a white tail just like the other demon. Was that Satan?

He watched them talk in silence, unable to hear anything being said, nearly panicking when the Demon-looking Rin jumped onto the human-looking one trying to kill him. Had this been what Rin was fighting against that whole time? His demon half. He looked a lot more menacing than Rin had. His aura just seemed to give off endless rage. But he seemed to back down against the older demon, it must be Satan. Rin had looked just like him…

Satan suddenly looked in Yukio's direction. Yukio flinched, could he see him? He thought he was invisible, but maybe only Satan has the power to see through the wall. He suddenly disappeared into blue flames, only to reappear beside Yukio. He jumped back, fear evident on his face.

"What are you doing hiding back here, little one? Did you come to watch the show?" He was unusually calm, but that same despicable smile was plastered on his face.

Yukio pushed himself back until he hit another invisible wall, he was trapped and had nowhere to go.

"Don't panic yourself, Yukio." Yukio flinched at the use of his name "I can't hurt you here, for neither of us is here physically." Yukio seemed to relax a bit at that, but did not let his guard down in front of the Demon King.

"W-Where am I? How did I get here?" He risked a quick glance in Rin's direction, both he and the demon were sat…talking it seemed. His attention was quickly drawn back to Satan when he spoke.

"We are inside Rin's mind; I have forced him into a state of unconsciousness so that he can converse with his demon half. The headaches are a bit troublesome for him if you'd noticed." Yukio nodded weakly.

"But why am I here, and why can't he see or hear me?"

"You are here as an observer; possibly through some link you share." Satan shrugged, he would investigate this more later. "Once the merge is complete, Rin will awaken, and we will be expelled from this space."

Yukio turned to look at Satan with a fearful look "Merge…?"

Satan was looking at the two Rin's, the demon apparently trying to make a wager and Rin seemed to be buying it. He grinned smugly.

"Hey! What do you mean?" Yukio asked again, still waiting for some sort of explanation. "What are you planning to do to my brother?" He frowned at the Demon King who just laughed in response, although in Yukio's opinion it sounded more like a cackle. A hint of the Satan he had seen before.

"I am but an observer like you. If anything happens it will be because they have agreed it. I merely brought Rin here because of the pain he was experiencing. All caused by your lies and hatred of demons." Satan glanced sideways at Yukio, whose fists were clenched tightly and shaking.

"He felt he had enough control over it to return home, so he found a way to escape – with help of Samael's meddling, of course. But being around you humans again just angered his demon half into trying to take action."

"You still haven't explained what this merge is." To be honest he had an idea, but was afraid to believe that his brother would actually go through with such a thing.

"Isn't that obvious? And here I thought you were the genius son." Yukio's frown deepened in his growing anger. He hated this demon, wanted to kill him there and then. But he was human and they weren't even physically here. Satan took in the boy's silence and continued.

"His human and demon egos are going to merge into one." Yukio's eyes widened with horror "So that there will no longer be fighting over who is in control of his body. So, you see. I only have my son's best interests in mind…Even if it does alter his personality and destroy what's left of his humanity."

Yukio's head snapped in Satan's direction, fear and anger all meshed into one. He jumped at Satan, going straight through him as he disappeared into blue flames. Yukio was alone again with only the receding echo of Satan's laugh to listen to. He ran back to the invisible wall, banging on it with his fists. He started to scream Rin's name before he noticed the two Rin's were fighting each other.

"Yes, Nii-san! Fight him!" He wasn't giving in to the demon, he was fighting back. Yukio felt elated at the thought.

Suddenly Yukio could hear everything that was going on, the silence had been lifted. Could Rin hear him now too? He yelled again, but to two were too preoccupied with the fight to hear his voice. He eventually sat in silence watching them duke it out, no fire; just a test of strength. It wasn't until partway through the fight that he took notice of Rin's face…he was smiling. The demon Rin had been smiling the whole time like he was having a ball. But Rin's had been concentrated and serious. What changed?

Rin's human ego started to take on more demonic traits as he fought the other, his ears grew pointed and fangs appeared. He then burst into flame and landing a solid punch on the other sending him flying through the darkness. The Demon didn't get up again.

"Heh...haha! I win!" He threw his arms in the air and fell to his knees laughing at finally having beaten the other. "I win. Now you have to go away and leave me the hell alone!" Rin spat towards the shadow of the demon.

"Nii-san!" Yukio tried again now the fight had ended, the invisible wall disappeared from in front of him and he fell forward to the ground. Rin turned to see his brother, surprise and wariness on his face.

"Yukio?" He slowly walked towards him. Yukio stood back up and moved towards Rin at a faster pace. He didn't hesitate this time and pulled his brother into an embrace. Rin froze for a moment before returning it.

"You Idiot." Yukio pulled back inspecting Rin's body for injuries "What were you thinking?" he scolded. Watching as the few injuries healed before his eyes. He took in the few demonic features that had appeared on the human version of Rin, wondering why they had appeared. Rin didn't seem to realise they were there. He just chuckled to himself.

"He said if I win, he'd leave me alone, and I wouldn't have to keep fighting him for control. The pain would finally stop…" He stared back at the unmoving shadow in the darkness. Feeling relief that it was over and his humanity intact.

"So, does that mean you can come home?" Rin looked reluctant, after what had happened before. "Rin, please I didn't mean to say what I said, we didn't want to hurt you. We just wanted to keep you safe." He gripped his brother's arm tightly "Please. Come home. You belong with Father Fujimoto and me."

"I don't think it'll be so easy for me to get out of Gehenna a second time, but…sure I'll try Yukio." He smiled; the first genuine smile Yukio had seen since he had disappeared that night two weeks ago.

The moment was cut short by a malicious laugh.

"How sweet, a touching moment for two brothers."

Black tendrils of shadow come out of nowhere and wrapped around Rin's wrists, body and legs; dragging him away from Yukio, who when trying to run after him was stopped by an invisible wall again. The Demon Rin emerged from the shadows, calling forth his flames and wrapping his arms around the human Rin's neck from behind.

"You forget the rest of our deal, my brother." Yukio looked to Rin confused whilst Rin was struggling against the bindings in a panic. He'd won the fight, so the demon had the leave him alone. The demon only won if he gave into to his demon urges, but he wasn't even sure what that meant!

"Let go of me!" He struggled more frantically than before. Panic starting to take over.

"What's he talking about Nii-San?!" Yukio panicked. "What deal?" Why did his brother make a deal with a demon of all things? Was he trying to be clever?!

The demon touched a finger to the pointed tip of Rin's ear before moving to his mouth to pull it open to reveal his fangs.

"Yup, proof right here. You enjoyed it!" He looked to Yukio and grinned. The same looking grin that he'd seen when Satan had entered Rin's body.

"His human ego took on demonic traits, as proof that he enjoyed the fight. Proof of his true nature. The deal was I would leave him alone if he won. BUT! If he gave into demon urges or in other words enjoyed the fight, if he relished the feeling of cutting loose. Then he is mine." He growled with excitement.

"N-NO!" Yukio screamed trying to break free of the cage, but it was no use.

Rin continued struggling against the bindings, tears forming in his eyes. He really messed up this time.

"So, now it's time! We even have an audience!" He cackled madly in Rin's ear. Rin looked in horror at Yukio, he would have to witness this, why was he even here! The demon got a firm grip on Rin's head, pulling it to the side so that the entirety of his neck was exposed to him. Rin's eyes locked to Yukio's tears running down his face.

He didn't want this!

He wanted to go home, why did he come back here!

Rin kept struggling before finally getting one arm free of the tendrils, but as he did so he felt the Demon's grip on him tighten and a sharp pain in his shoulder as fangs bit down deep. He screamed one last time, looking into Yukio's eyes reaching his arm out for him.

"YUKIO!"

Before his eyes went cloudy and his body slacked against the remaining bindings. The demon ego smiled menacingly at Yukio as he seemed to merge himself into Rin's human form. His hair turned back to white, all his demonic features returning before the bindings disappeared and released him, his body fell to the floor.

Yukio tried to yell for him to get up, but the more he tried the quieter his voice went before everything including Rin faded to darkness.

Yukio woke up screaming Rin's name, with Shiro next to him trying to shake him out of it.

"Yukio! Snap out of it!"

He registered the voice and turned to Shiro, he was shaking all over and covered in sweat.

"Yukio? You look like you've seen a ghost…"

"Something terrible has happened…" Yukio whispered.

"Yukio it was just a bad dream, you're safe now." Shiro held him close, he'd never seen Yukio this scared since he was a child.

"N-No, it wasn't a dream. It was Rin, I was in Rin's mind…Satan was there…" He struggled out of the tangled bedsheets, sitting up in Rin's bed. Yukio was never this badly shaken anymore, it must've been serious. If Rin and Satan were involved, it made him more curious.

"Ok, tell me everything."

Well...this took a bit of time. Honestly this started out in planning as a mutual merger...but yeah... sorry(not sorry?).

Once again thanks you for all the comments/reviews/follows/faves and kudos! If you notice any errors please let me know (I swear I've read through this thing like 20x times and I still miss things.)