I would like to see someone take revenge on Kristoph (while he's in prison) by slipping him some slow-acting poison and proceeding to have non-con sex with him while he's dying. The perpetrator can be absolutely anyone anon wants.

However, I'm flexible, so if anon is uncomfortable with either sex or dying, the sex can be replaced with taunting and watching Kristoph's desperation, and the death can be fixed with an antidote once he's got a taste of his own medicine. All I actually care about is Kristoph being poisoned and not liking it.

Atroquinine, My Love

A song hovered eerily in the air from a small stereo in the corner of the cell. Klavier Gavin tried not to smirk as he handed his seated brother a glass of scotch.
"Thank you for visiting, Klavier," Kristoph nodded, taking a sip from the glass, "It's been a while. I assumed you'd chosen to deny my existence."
"Well, we are family after all, mein bruder," he replied, sitting in an armchair opposite him, "What was I to do? Let you rot here all alone?"
"Why the sudden concern for my social welfare?" he asked suspiciously, arching an eyebrow and pushing his glasses atop the bridge of his nose.
"Who do you think I am, Kristoph?" he asked calmly.
Kristoph suddenly started trembling wildly and coughing violently.
"Perhaps you mistake me for you, brother," Klavier smiled, imitating his brothers' usual sinister sneer.
"K-K-Kla... What's happening... to me?" he panted in between strained wheezes.
"Just enjoy the music, baby," he replied casually.

Atroquinine, My Love
Whatcha doin' to me, Baby?

"You... you... Klavier? You... poisoned me?" Kristoph panted, clawing desperately to remove his tie.
"Let me help you there," he smiled with disturbing softness, as he gently removed the tie and walked across the cell to place it on the table.
"Klavier, please!" he cried out, growing pale.
"Shhhh, shush, Kristoph," Klavier laughed, "You look silly like this!"
"Klavi, I... Ich... bitte! Bitte! Mein bruder!!!" (I... please! Please! My brother!)
"C'mon, Kristoph, let's relive some memories, ja?" he continued, pulling his brother onto his feet. Kristoph clung to the lapels of his younger brother's jacket.

Atroquinine, My Love
Whatcha doin' to me, Baby?
Your deadly lovin' is driving me crazy

"Let me take off your glasses," Klavier sighed, gently removing Kristoph's glasses and placing them on top of the tie.
"Klavi, warum?" (Why?)
"Ja, I recall that's exactly what I said when you did this to me," he smiled through mildly gritted teeth. He dragged his brother across the cell and pushed him against the bars. "I know there weren't bars, bruder, but we've got to work with what we've got, ja?"
"Bitte bitte bitte... Ich weiƟ nicht..." (Please please please... I don't know) he mumbled, his face in between two bars.
"I didn't know either back then," Klavier sighed, "I was eight, you were sixteen." And with that, he wrapped his arms around his brothers waist and unbuttoned his jacket. "You were twice my age." He tore it off and flung it to the floor. Now, he had access to Kristoph's belt. "The first time you did this to me, anyway." He unhooked it then threw it to the floor. The trembling older man's trousers fell to the floor.
"Klavier, what the fuck are you doing?!?!" Kristoph managed to cry out, physically incapable of doing much else.
"Nothing my big brother wouldn't do," he whispered into his ear, groping around his brother's body until he reached a bulge in the front of his black briefs. "Are you getting off on this, bruder?"
Kristoph choked as a tear slid down his cheek. His throat felt like it was burning and he started feeling weaker. He clung to the bars.
"You're quite sick, aren't you, bruder?"
"You're the fucking sick one, Klavier!"
"Oh, ja?" he hissed, tugging down the tight underwear.
Kristoph hissed as the cold air rushed past his exposed erection.
"You're thirty two. Thirty two and a rapist. Thirty two, a rapist and a murderer," Klavier growled, unzipping his flies and smoothly setting free his own erection, shielding it with a condom he'd had in his pocket.
"You'll be! You... you're planning... those... right now!" he screamed, his back arching against his will.
"You're not eight, you sick fuck!"

Atroquinine, My Love
Whatcha doin' to me, Baby?
Your deadly lovin' is driving me crazy
You're killing me, Baby, Killing me

Kristoph was falling further to the effects of the poison. He couldn't quite get any words out. There was, however, very little he could say to free himself from his punishment anyway.
"I hate you. I hate you so much, Kristoph," Klavier growled. He spat into his hand and rubbed his cock before positioning himself behind his falling brother, "But for some fucked up reason, I love you. I love you. Ich liebe dich. Ich liebe dich! ICH LIEBE DICH, MEIN BRUDER!" (I love you. I love you! I LOVE YOU, MY BROTHER!)
He began to cry. Kristoph let out a surprised whimper as he felt a cold tear drop stain the back of his own painfully contorted neck.
Crying hysterically, Klavier thrust into his brother's resisting hole. Kristoph hissed as he was being skewered. His whole body felt as though it was on fire. Klavier kept thrusting, hard and deep, pounding him into the metal bars. He lost control, bucking his hips and roaring through his tears like a caged animal. On the other hand, Kristoph was becoming more and more like a corpse. All that was supporting him was his brother's dick, slamming him against the bars.
"This... this is... for everyone you ever... ever... hurt... Which, let... let me tell you, bruder... It's a lot of... lot of people!" he cried, slowing down slightly, "Herr Wright... Herr and Fraulein Misham... Herr Enigmar... Me... and mein Herr Forehead... my Apollo... I know you did the same to him as you did to me! Maybe not when he was... Gott, makes me feel sick. You make me feel sick."
He pulled out. Kristoph slid to the floor, still clutching feebly to the bars. Klavier unfurled the condom and threw it on the heap of brother lying beneath him.

Atroquinine, My Love
Whatcha doin' to me, Baby?
Your deadly lovin' is driving me crazy
You're killing me, Baby, Killing me
Atroquinine, My Love

"Did the news get to your cell that there's an antidote for atroquinine?" Klavier asked softly, tidying himself up.
Kristoph simply wheezed.
Klavier sighed, pulled a miniscule vial from his pocket and knelt down at his ailing brother's side. "Open your mouth, leibe." (Love.)
He tried to follow his brother's orders but was too weak. Klavier rolled his eyes and administered the antidote himself. "There."
Kristoph coughed.
Klavier looked at him sadly for a moment then sighed and started pulling up his brother's underwear and pants. "I'm sorry, bruder." He held him in his arms for a little while, crying onto his back until he felt him start to move.
"Klavier... wie alt sind sie?" (How old are you?)
"Kristoph... ich bin vierundzwanzig jahre alt..." (I am twenty four.)
"Aber... mein Klavi ist sieben jahr alt..." (But... my Klavi is seven years old.)
"Wie alt bist du?" (How old are you?)
"Ich bin funfzehn jahr alt." (I am fifteen years old.)
Klavier gave a heavy sigh as he looked at his brother's puzzled face. He hadn't expected this. He knew what he'd planned was completely wrong, he was quite sickened that he'd even contemplated such a thing. But he hadn't expected, for even a moment, that Kristoph would succumb to a delirious regression such as this. For that moment, it felt as if he was looking at the Kristoph he once knew. The kind, caring brother he'd loved so dearly.
The moment was fleeting. With another cough, Kristoph's bemused expression turned to one of anger.
"Oh, Klavier..." he tutted, starting to sound a little more like his more recent self. "You think you're so clever, don't you? Well, let me tell you something, bruder. Once my body has recovered from your... hilarious little prank... well, let's just say, if you even live through what I do to you, then you'll live to regret what you did to me."
This remark reminded Klavier exactly why he'd done this. To humiliate this... demon.
"That suits me fine, Kristoph. Because I never want to see you again."

Atroquinine, My Love
Whatcha doin' to me, Baby?
Your deadly lovin' is driving me crazy
You're killing me, Baby, Killing me
Atroquinine, My Love
Your love is a poison an' I can't take no more