I wanted to do a little one-shot about Amaimon before, because I feel like he must have some seriously messed up stuff going on inside his head. Then I had this thought, demons aren't part of God's domain, and it says when they possess a being that can interact with Assiah eventually they will rot away. Perhaps they can feel that rot, perhaps it is one of the things that makes Amaimon so crazy all the time - not just Amaimon, wouldn't Mephisto feel it too?
Ahaha ignore my musings. ORZ

The Ache

The ache was dull yet ever present. It throbbed, ebbed and flowed throughout his body – maybe, maybe, maybe – if he chewed off his fingers it might go away. That itch, that burning sensation that drove him insane with each passing second.
Sometimes it felt as though a parasite had rooted itself inside of his brain, behind his eyeballs, and it took all of his willpower not to push to force his talon-like nails into his irises to reach the creature inside.

He would follow the searing with his eyes, from his brain to his chest, then his legs, back up, his arms to his fingertips and then – chomp. Blood, pain, anything was better than this. There goes another nail-bed; this time maybe he would take the whole fingertip.
The feeling grew closer, closer, suffocating tighter, tighter, until he could no longer take it. Piercing azure pools stared miserably at his hands, the Earth King was now missing the top section of his right index finger.

It still wasn't enough. It would never be enough. This body was weak in Assiah, this body was rejected, despised, God's very nature commanded him to destroy it – so he did, from the inside out.
Was he insane? Did his brother deal with this every day? These questions may have all been asked at the same time, or they may have been rattling around for hours. The clock-face was so irrelevant, so abstract that no sense of time or even presence greeted him.
Finally, slowly, slowly, he lifted his left hand, and his remaining index finger was pointed at his eye so casually. This would be it; he could take the parasite out and be done with it.
A sound filtered in from the distance. What was it? A voice, a name, someone was calling him.

"Amaimon!" The shouting was frantic, insecure, worried even. He knew that voice, who did it belong to? It didn't matter; all that mattered was the ache.
The ache.

"Amaimon, stop it! You're fine, pull yourself together. Did you seriously eat your own finger?!" it was his brother. It was Mephisto.

"Aniue..." He came back to reality, or at least their current reality, with a loud bang. A piercing scream rang out from his throat; it rose to a chilling pitch before descending back into silence. He clutched at the disarticulated stump of his digit, which bled profusely. He hadn't even been aware he was drinking the blood.

A sharp slap registered across his cheek, and then the other; his brother was hitting him with his glove. What was he doing? He'd grabbed his hand now, the pain came back even stronger, and he tried his best not to whimper. Then it was gone, it was buried under wet warmth. It was a cloth, aniue was cleaning the wound, he'd put some kind of bandage on it now. It felt so much better, but the ache, the ache was stronger than ever.
The ache.

"Ani..." he mumbled, clutching at the other for support, still lost inside his own head, trapped within his thoughts and that burning, that insatiable itching that only calmed with violence. Something else was said to him but he didn't hear it, he was sinking further away by the second.
Stop! Help me! I don't know where I am, brother! No words came out of his mouth. Instead he felt something touch his head, he held on to the sensation, praying it would help tether him to what little sanity remained.

The feeling began to take form, yes, it was Mephisto, and he was stroking Amaimon's head. Next, images came into focus – he could see his beloved big brother! It was sounds that came last, but he still held on tightly to the form in front of him, he clung to the last vestiges of hope that the sensation brought.

"There, see, calmer now aren't we~?" asked the familiar cock-sure voice of his kin. "Maimon, you must learn not to give in to these things." His brother was always so helpful, always knew what to do.

"Do you feel it?" asked the Earth King, risking a glance up at green orbs with his own blank seas.

His brother's expression softened, it was remorseful and bitter. It was a face he did not often make.

"Do you want the truth, or shall I make it go away?" it was a question that required an answer.

"Please tell me aniue."

It was silent for a long time, before Mephisto finally replied, pulling his younger brother closer and burying his face in the crook of his neck.

"Every day. Every hour. Every second."
This resulted in Amaimon clutching him tighter, feeling as though he might explode. His brother also had to feel this way; he also had to suffer this endless torture for centuries.

"How do you make it bearable..." it was more of a statement than a question, but Mephisto replied anyway.

"Why do you think I called you here from Gehenna?"

Answering with another question.

"I don't know... Because you wanted me to help you?"

"I am selfish to make you stay... You can leave whenever you wish."

Amaimon was not pleased with the lack of answer.

"Ani, why did you ask me to come here?"

His brother took his face from Amaimon's neck and leaned in close to his face, planting a soft kiss on his cheek.

"Because, at least for the moment, this will stop my ache." Finishing this statement by pressing his lips hard against the other demon's, it was only a matter of time before he would kiss back.

Yes, like this, at least together, for an hour or so, they could stop their aches.