Shadowhunters || Jasmodeus || The Mark of Asmodeus || Jasmodeus || Shadowhunters

Title: The Mark of Asmodeus – Writer's Month 2020

Fandom: Shadowhunters: The Mortal Instruments

Disclaimer: All rights to the Shadowhunters show reserved to Ed Decter, the books the show is based off and its characters belong to Cassandra Clare. This fanfiction on the other hand is entirely mine. No money is made with this, though reviews are more than welcomed.

Tags: m/m, poisoning, magic, hurt/comfort

Main Pairing: Asmodeus/Jace

Shadowhunters Characters: Jonathan Christopher 'Jace' Herondale, Asmodeus, Magnus Bane

Writer's Month Prompt: poison

Summary: Lilith poisoned Jace with the very essence of Edom. Magnus makes a deal with Asmodeus, to keep Jace safe until Magnus can find out an antidote; because in Edom, the poison stops spreading.

The Mark of Asmodeus

Writer's Month 2020

"Well, well, well. I did not expect you to summon me, son."

Magnus glared at his smugly grinning father. If he'd have a choice, he wouldn't have. But Alexander and the puppy-dog eyes, Magnus' own helplessness, the fact that Jace was getting worse by the hour – this was the only chance. As much as he loathed it.

"I... need your help", stated Magnus with gritted teeth. "He was poisoned by Lilith, with an essence from Edom. Take him to Edom, where the poisoning will stop. Just keep him there, nothing more."

Asmodeus regarded him thoughtfully and tilted his head. "...Very well."

That did surprise Magnus a bit. He hadn't expected this level of cooperation, especially not without a bargain. He had expected his father to make a deal, to force Magnus to release him from Edom.

"What? Doing you a favor may soften you up the next time I want something", drawled Asmodeus. Magnus raised a suspicious eyebrow at that, but sadly he had nothing to argue about here. He needed Asmodeus' help. Otherwise Jace was going to die again, this time for good, and if Jace died, Alec would never recover from that. Magnus would never forgive himself either, if there was anything he could do to stop it. Jace had been brought back from the dead by the Angel and it had left him weak, weak enough for Lilith – summoned by Jonathan Morgenstern with his last breath – to slip into his mind and poison him, with the essence of Edom itself. It was a slow and definitely deadly poison, outside of Edom at least. The only way to stop it was to be in Edom, the only antidote was somewhere in Edom – but for that, they'd have to find out what Lilith used exactly, which minerals and plants and demon-parts. Magnus needed time to figure that out, time he didn't have, not while Jace was up here. In Edom, the poisoning would stop, giving Magnus time. He had drawn enough of Jace's blood to do his research.

"Watch over him", requested Magnus. "Do not let harm come to him."

"Yes, yes. You have my word", promised Asmodeus.


Asmodeus had a flare for the dramatics, so he placed the comatose Shadowhunter on a glass-coffin, held together by golden patterns like vines, with beautiful leafs. Naturally, the blonde Shadowhunter had to match his new coffin, so Asmodeus gave his clothes an upgrade – a white suit with gold patterns that matched the coffin, his hair gently falling around his face on the white satin pillow. He was pretty to look at, Asmodeus had to admit that. But just looking at him got a bit boring after a few days. Very pretty indeed, but so boring. He wasn't doing anything, after all. On the fifth day, Asmodeus decided to wake pretty blonde up so he could entertain the king. The demon raised his eyebrows intrigued when dual colored eyes fluttered open. Slowly did the young man sit up and look around with those mismatched eyes of his, a curious expression on his face.

"What... happened? Where am I? Who are you?"

"Easy", whispered Asmodeus in a seductive tone. "An evil warlock cursed you. I brought you to my castle and woke you from your slumber with True Love's Kiss."

The Shadowhunter looked around again, with narrowed eyes, before settling on Asmodeus. "Right, Prince Charming. That's very believable. Now the truth."

"Technically, King Charming", corrected Asmodeus amused. "My son put you under a spell, a magic coma you could say, to slow down the poison in your system. However, seeing as it won't spread any more in my realm at all, I figured I could wake you up, so you can entertain me."

"...Entertain you, huh", grunted the blonde as he sat up some more, looking at himself. "Well, you got taste, I got to hand you that mu... You said son. Y... You're Asmodeus."

"Mh, my reputation precedes me", hummed Asmodeus pleased. "Alas, you have the advantage then, because my son clearly lacks manners. He didn't tell me your name."

"Jace. Jace Herondale", supplied the blonde, running his fingers through his hair.

He leaned back, supporting himself with one hand and looking around once more, taking in the glory of Asmodeus' castle. It made the demon king smile pleased. He knew his castle was impressive. Mismatched eyes wandered to check how to get out of the glass-coffin.

"...Give me a hand?", requested Jace doubtfully. "Why a glass coffin?"

"Fun", shrugged Asmodeus with a tilted head, offering a hand.

He helped Jace climb out of the staged glass-coffin. Jace straightened up and looked at Asmodeus once more. He was shorter than the king, not by much but by enough to amuse Asmodeus.

"What's going on?", asked Jace after a moment. "Am I... dead?"

"So dramatic. I like you", laughed Asmodeus. "No, you're not. From what I gather, you were poisoned by Lilith. The poison was created here, in Edom. It has no effect here. Magnus brought you here to stop the spread of the poison until he finds a cure for you. He asked me to keep an eye on you. I put you there, bit like a... piece of art? Nice to look at. But a little boring, you know. So I thought, I could wake you from your coma, that way you could entertain me some."

"You keep saying that. What do you expect of me?", asked Jace warily.

"Mh. You're a Shadowhunter, aren't you? It could be entertaining to watch you battle a lower demon or two", suggested Asmodeus after a moment, tilting his head.

"Well. I've been laying in my sick-bed for days before Magnus put me in the coma, so I'd like some action", agreed Jace. "Bring it on, Prince Charming."

"Again: King", corrected Asmodeus with one raised eyebrow.


Jace was good entertainment indeed. He fought bravely. His movement was graceful, precise, beautiful to watch. He loved watching the blonde fight whatever demon Asmodeus summoned for him. They had come to fear their 'sparring duty', though Asmodeus promised them no death (how boring). Alas, just watching him fight became a bit repetitive after a while too, so he started talking to the blonde. Using Jace to catch up on the surface world and the Shadow World's latest gossip.

He learned about the war, Morgenstern, what had all unfolded – and Jace's role in it. Fascinating indeed. The boy was interesting. They started talking about more than just the Shadow World. It turned out that Jace was well-read and Asmodeus liked a good book – had done so since books were invented, really. Alas, not many liked to read down here. A good conversation was so hard to come by in Edom, really. So the two of them talked and talked for hours. They started playing chess too, because Jace was a good strategist. Asmodeus started looking forward to spending time with Jace, whenever he was in a meeting with other higher demons, he found himself wanting to spend time with Jace instead. It had been a very long time since Asmodeus had last found someone he enjoyed spending time with, but every single day he spent with Jace, he wanted more.

"Dance with me", requested Asmodeus with a charming smile, offering a hand.

Jace was an exquisite musician – he oftentimes played the piano for Asmodeus. Tonight, however, Asmodeus wanted to see the grace and elegance put to use in a different way. For a moment, Jace paused, though then he accepted the hand and let Asmodeus lead him in a waltz.

"What is this?", asked Jace softly as they floated over the dance-floor.

"A waltz. I would have thought you knew that", chuckled Asmodeus.

"No. I mean... why are we dancing with each other? I'm your company. But... this feels... much more... intimate than how we usually spend our time", pointed Jace out.

"So observant", whispered Asmodeus pleased. "It's what I like about you, dear. You are bright."

"You like me, mh", grunted Jace, narrowing his eyes at the demon.

"Well, yes. I suppose. You could... entertain me... in other ways too."

Asmodeus' voice was a low lull as he leaned in, slowly. His lips brushed past Jace's cheeks as he whispered into Jace's ear, making the blonde shudder in a pleased way, clinging onto the king at the filthy, seductive things that Asmodeus suggested until Jace's knees grew weak.


Asmodeus' bed was nice. It was large, soft, comfortable, with a beautiful view on all of Edom through the large windows that oversaw the king's lands. When he had woken up in a glass-coffin he thought things would go downhill from there. Instead, he found himself very intrigued by the demon. They got along surprisingly well. It was nice to not be underestimated for a change. Everyone in New York scoffed, thinking his book club was only a euphemism – and, sure, he had slept with many members of his book-club but the book-club was still real. He loved reading, classics, fantasy, science fiction; not just the literature required for Shadowhunters. Asmodeus appreciated his intellect, they talked for hours. They played chess, Jace would play the piano for Asmodeus to 'amuse' the king whenever he has had a hard day and simply wished to sit and enjoy his wine. The dance last night had surprised Jace. Even more so what had followed.

"You are awake", noted Asmodeus pleased, tracing Jace's face with a hand.

Asmodeus was handsome. Charming too; it was obvious why he was the demon of lust and seduction. Yet this didn't feel like a con. Jace had been staying here for ten days now. If sex was all he wanted, Asmodeus could have gotten into Jace's pants on the first day, honestly. However... this seemed to have come as a surprise to Asmodeus too. The attraction between them.

"Good observation skills, Prince Charming." Jace rolled over to lay on Asmodeus' chest.

"If... I were to heal you, will you come back to me?", asked Asmodeus in a low voice.

"W... What?", asked Jace surprised, sitting up some.

"I'm the king. I can heal you from the poisoning essence of Edom. But then you will... leave."

Jace licked his lips, staring down at the king. He had never felt this connected with someone. Treated like an equal. He enjoyed being with Asmodeus, more than he would have ever expected. Slowly did he lean down and kiss the king. A gentle, soft kiss.

"Yes", whispered Jace against Asmodeus. "Someone's gotta keep the king entertained, mh?"

"Someone has, indeed", agreed Asmodeus pleased, laying an arm around Jace's waist.

Jace laughed softly, nuzzling his face into Asmodeus' neck. Why...? Why was the king of demons making him feel this way? Understood, connected, valued. He yelped a little as Asmodeus rolled them over and pinned Jace on the bed, by pressing his hand against Jace's chest.

"Up for a second round, Charming?", asked Jace curiously, raising one eyebrow.

"Naughty little Shadowhunter", hummed Asmodeus bemused. "No. I'll heal you."

Jace raised his eyebrows. He had expected an antidote of sorts, not... this. Whatever this was. Asmodeus was leaning over him, resting his spread-out hand right on top of Jace's heart.

"There is no antidote for what Lilith did to you", explained Asmodeus, causing Jace to freeze. "The only cure is Edom itself. It is Edom's essence. Being here has healed you – for as long as you are here. What I can do to heal you is... mark you as mine. As a part of Edom. You will carry my mark, my essence and power, with you wherever you go, even the surface world."

"What... your mark", echoed Jace with his voice wavering.

"It's your only option. You can stay here forever, or you let me mark you", offered Asmodeus.

"What does it mean, exactly? I need more explanation", requested Jace.

He wrapped his hands around Asmodeus' hand, holding it in place while staring deeply into the beautiful amber cat-eyes of his demon king. Asmodeus smiled slyly and leaned in to kiss him.

"It marks you as mine. Any demon facing you will realize that you have been claimed by the king. They will know better than to touch what is mine. You and I will be linked, similar as to this mark of yours", replied Asmodeus, playfully poking Jace's parabatai-rune with his free hand. "It connects us. I will feel when you are in distress, when you call to me. You will not need any rituals to summon me, simply your will. You will be able to travel back and forth between Edom and your world however you desire. I don't know just how much it will affect you in regards to magic – if you will simply be more in tune with magic, or if you will be able to access my magic, to a varying degree. With my magic embedded in you through my mark, you carry a piece of Edom with you and with that, the poison in your system is rendered permanently ineffective."

Jace frowned, staring from the hand up to Asmodeus' face. "Is that... I want to believe you're doing it because you've grown fond of me, but... this is your way out of Edom. From everything I know about you from Magnus, he would never forgive me if I give you a 'get out of Edom free' card."

"Perceptive", whispered Asmodeus, his voice a low purr as he leaned in to kiss Jace's temple. "It's what I enjoy the most about you, dear. Yes, the link between us will allow me to follow you wherever you go, including the mortal realm. It would be my... get out of Edom free card, as you say. But it is also your only chance, dear. Very well. Think on it, beloved."

He kissed Jace's temple again, while Jace's heart did odd things at being called 'beloved' by the king. But no; Jace knew how much it must have taken Magnus to even ask Asmodeus for help. Jace couldn't strike this deal, even if it was the only thing that could save his life. Not without talking to Magnus about it. Licking his lips, Jace rolled over a little, onto his side.

"Can I talk to Magnus? I mean, is there a way...?", asked Jace softly.

"I can call my son here", replied Asmodeus. "I can't promise he'll show though. Our relationship is... a bit... rocky, to say the least. But if I tell him you ask, maybe he will."


Magnus paced the meeting hall in Asmodeus' palace. His father had requested his presence; not because he wanted to talk to Magnus, but because he claimed Jace wanted to talk to Magnus. Why would Jace even be able to talk to Magnus at all? He was supposed to be in a coma. Magnus had merely meant to store Jace in Edom, for safekeeping.

"Why are you up on your feet? That's not how I left you here!", exclaimed Magnus displeased.

Jace immediately ducked his head as he was being chided immediately. "Hello, Magnus. Nice to see you too. Your dad grew bored just looking at me as a piece of art, so he reanimated me."

The blonde paused when he was being pulled into a tight hug by Magnus. "I was so worried about you, blondie. You can't just nearly die on me like this. It'd devastated Alexander."

"Alec. Sure", huffed Jace with a small, teasing smile.

Yes, it would absolutely wreck his parabatai – but the hug, the look in his eyes and the wavering of his voice told Jace that Magnus himself would be pretty devastated himself. Jace smiled to himself as he returned the hug. He was aware of Asmodeus standing in the background, watching.

"So. Funny thing happened while you were busy trying to figure out how to heal me", drawled Jace.

"...You hooked up with my father", sighed Magnus exhausted after only a moment. "What? Don't look so surprised. I lived with you long enough to know you. And I know him."

"Well, it's a bit more than that", offered Jace softly, before blushing. "I mean – I'm not talking about that, I mean the poison. Your dad says that it's... the essence of Edom. There is no cure."

Magnus averted his eyes in a way that was very telling. "I... I have been researching everything, trying everything... there has to be a way. I will find a way, Jace."

"You won't, son. And you know it", pointed Asmodeus out. "Lilith designed it this way. To hurt you and him the most. The only way he survives would be to choose banishment to Edom. Or-"

It was fascinating to see Magnus piece the parts together, his eyes widening in shock. "No. Jace."

"It's why you're here, Mag", offered Jace softly. "Charm – Asmodeus has explained it to me. The Mark of Asmodeus will tie us together, will allow him to... come and go as he pleases. I can't allow that, not without talking to you first. I... can stay here. I'll live, right? I'm fine here."

That gave Magnus pause though, because Jace seemed to mean it. He was fine being here. The fact that Jace was genuinely fine living in Edom, it told Magnus volumes about the way Asmodeus must have treated him here in the past two weeks. Furrowing his brows, Magnus looked at his father. Their past was their own, whatever Asmodeus and Jace had was – was theirs. And from the look on Jace's face, it was good. Magnus narrowed his eyes as he started at his father.

"If you ever hurt him, I will banish you to limbo myself. After giving Alexander a chance to give you a piece of his mind and believe me, you should fear his wrath even more", warned Magnus. "And I will not stand aside with whatever troubles you cause in the mortal world either."

"So I have permission to mark what is mine?", asked Asmodeus amused.

He wrapped an arm around Jace's shoulders, resting his hand above Jace's heart. The blonde blushed, but he also instinctively leaned into the demon; a motion that wasn't lost on Magnus.

"You really have fallen for my father", muttered Magnus stunned, shaking his head. "And here I thought you displayed bad taste when your ex turned into a serial killer."

Jace huffed and elbowed him, though his cheeks were flushed a shade of pink. Magnus crossed his arms, motioning for his father to go on. He was going to oversee this and then he was going to take Jace back home to his fretting parabatai. And he was going to have a serious conversation with Jace about caution and what to watch out for with Asmodeus – particularly with his magic.

"Jace", whispered Magnus once more, while Jace was unbuttoning his shirt. "The link means more than just that, you do realize that, right? It... binds you to my father for eternity."

"Immortality. Yeah, I read between the lines", nodded Jace with a tilted head. "I really am not as stupid as many assume when looking at my pretty face. The thing is, my parabatai is kind of dating an immortal and I know sooner or later, he's going to find a way to cheat death for that purpose too. There's probably like... a Mark of Magnus or whatever coming his way. So... that's gonna save him an eternity of heartache too, isn't it? Now stop fretting. I considered every angle, for my sake. It was... your sake that I was worried about. You're really fine with this?"

Magnus raised an unimpressed eyebrow as he regarded his father and nodded. Asmodeus smiled at him while he performed the spell, burning his mark into Jace's skin, the sigil of Asmodeus. The only way to cure Jace and return him to his world. The mark that would bind him to his lover for forever.

~*~ The End ~*~

Author's note: This was fun to write! Took me a while to figure out what I wanted to do with the poison prompt, but I'm pleased with the way it turned out!