Until the World Burns Down—A Mortal Instruments One Shot Fanfic

A/N: This was written for a friend of mine who has been begging for some Simon/Izzy love for a very long time. Hope you enjoyed it. All characters are the sole property of Cassandra Clare. Anime references are not mine either. I just like to dabble. No copyright infringement is intended.

What could she say about Simon Lewis that hadn't already been said?

Vampire.

Geek.

Hero.

Combined, they sounded a lot like the name of Eric's next band; either that or the makings of the greatest video game ever known. But there was one word that no one had used to describe the boy sitting across from her at Taki's, sipping on what, Simon called, a Blushie.

That word was charismatic.

Simon had a way about him that captured her heart.

Sure, he had his moments—especially right now as he played with his dinner—when Simon was a little too vulgar for Isabelle's tastes. But a part of her craved that playful nature, as if the troubles of the outside world meant nothing when they were together.

Simon made her laugh.

She was drawn to it like a moth to a flame.

"You know, I think I'm going to trademark this," said Simon, jabbing the bloody concoction with a straw.

Isabelle Lightwood rolled her eyes. "Good luck with the patent office. I doubt they have much call for vampire cocktails," she laughed.

"Hey, don't knock my blood slushie until you've tried it," he joked before taking a long draw of the sloppy mixture.

Isabelle grimaced and looked down to her half-eaten salad, suddenly no longer hungry for what she never should have ordered in the first place. Coming here had been Simon's idea; he wanted to talk about everything now that Sebastian was free in the city and Simon's mark had vanished.

Isabelle feared the worst.

Was Simon hiding something?

"Trust me, I have no intentions of trying it," gagged Isabelle as her dark eyes met with his. "Now, quit stalling and tell me what we're doing here."

Simon's hands tightened around the glass. Isabelle was certain that he'd grown three shades paler, if that were possible for one of the Night Children. He seemed paralyzed, like a deer caught in the headlights of an oncoming car. "Simon?" she mumbled, wondering if he was going into some kind of vampire shock. "Earth to Simon. Hello?"

"Yeah, uh, give me a sec," he muttered.

Patience had never been her strongest suit. As Simon shuffled in the booth and nervously smacked his lips together, irritation began to seep into Isabelle's mind. "Any day now," she griped, staring at him for an explanation.

"Look, this isn't easy for me to talk about," answered Simon, who immediately pushed aside his Blushie and turned his deep, coffee-colored eyes on Isabelle. "Do you remember when we were at the lake…just after the angel disappeared?'

"Of course I do. It was only last week," she huffed, shaking her head from side to side.

"Do you remember what we talked about before Magnus interrupted?" he asked, as if she couldn't recall every single detail of that fateful night.

"Does it really matter?" she groaned, poking at the meal she had no intentions of eating.

Isabelle remembered everything. The way her heart had clambered in her chest when Simon had fallen to the ground, the overwhelming sense of relief that had bounded through her when she realized he was still alive—well, as alive as a vampire could be—and how Simon's mark had been taken in exchange for Michael's sword. She also remembered how she had clung to Simon as they toppled over into the wet sand; she hadn't wanted to let him go.

"I think so," he carried on. "Clary brought up something very unusual a few days ago. I was hoping you could help me to understand it."

"Oh, and what did Clary have to say?" Isabelle still had mixed feelings on the whole Clary thing. There was no room for Isabelle in Simon's heart if he refused to let his love for Clary die out.

"Could you please put aside your hatred of Clary for one second? God, it's like you're trying to stake your claim," groaned Simon, his hands tugging on loose brown curls that had fallen into his eyes.

"I am not staking anything. Least of all you," Isabelle snapped.

"I see. Very funny." Simon's eyes narrowed. "Maybe I came to the wrong person about this."

Suddenly, a light bulb went off in Isabelle's head, and she went rigid in the old booth. "Wait a minute. You said God."

His lips curled, loosening his taut face just a smidge. "Ding, ding, ding! We have a winner," Simon announced to the meager crowd sitting around them. "Please get Miss Isabelle Lightwood a prize!"

"How?" Isabelle breathed out, ignoring his chants and applause.

She knew he was no longer cursed, but this odd turn of events was startling, even to her. She'd only heard one vampire utter the name God, and that woman was as dead as Valentine himself.

"Clary thinks that by believing I am not cursed—or dammed—that somehow I'm not forbidden from saying his name. I'd really like your opinion, though," explained Simon with a hopeful look in his eyes.

Simon wanted her opinion? A flutter of happiness danced in Isabelle's stomach; she had a hard time concealing the jubilation as she prepared an answer. "I guess I have to agree. You've changed since meeting the angel, and he did tell you that you were a warrior for Heaven," she concurred.

"It's a lot to process. I-I've been having some trouble wrapping my head around it," admitted Simon as he flicked a crumb across the table.

Isabelle saw the pain in his eyes. She knew how hard it was to believe in one idea, only to have it completely overturned the next day. She had once felt as he did, when her mother spoke of how men were not to be trusted. Growing up with that notion planted firmly in every thought you had was hard enough. But then to come across someone like Simon Lewis and have that ideal blown completely out of the water had shaken Isabelle to the core. Granted it wasn't exactly the same situation—comparing her love life to that of the angel's call was like saying romance was more important than divine intervention—but it was all Isabelle had to work with.

"Maybe you're overthinking it," she proposed, wondering if a distraction might ease away some of his nervousness. She would do anything for Simon. He meant everything to her now, especially if Sebastian insisted on wiping out the entire Shadowhunter world. "Forget about it for a while. Just have some fun."

"Fun?" Simon's eyebrows lifted in surprise. "Sebastian's on the loose, Jace is a walking glow stick, my mark is gone, and you want to have some fun?"

Isabelle shrugged. "Who knows when we'll be able to do this again? The world could burn down tomorrow, and then you'll be saying 'Why oh why didn't I listen to Isabelle'," she smirked, hoping that he'd take the bait.

Isabelle wanted Simon alone, away from gawking warlock eyes, away from all this chaos. Tomorrow would come soon enough. Why waste tonight? She craved the chill of Simon's lips, the thrill of his teeth piercing through her skin again.

She needed Simon.

There was no other way to put things.

It was a simple matter of need.

"Well?" she barked, tapping her foot on the checkered floor beneath the table.

A smile washed across his pallid face. "Okay, what did you have in mind?"

They'd taken the long way back to Simon's apartment, laughing and holding hands as though they were a couple. The moon had guided their adventurous stroll through Central Park, where Isabelle had threatened to chuck him straight into water after he'd joked about how her black dress wasn't flattering in the least. Truthfully, it made Isabelle appear older and wiser and pretty darn sexy overall.

He'd had a hard time keeping it together between his hunger and that dress.

Simon's stomach gurgled.

He should have finished off that Blushie instead of leaving Taki's with Isabelle.

Now, she was sitting on the edge of his bed, thumbing through one comic book after the next. And Simon was practically starving.

He knew that she detested anything to do with the world of anime, but it was the thought that mattered most. Isabelle really was trying to take an interest in his life, despite the troubling world around them that never seemed to ease up.

"You really like girls that look this way?" asked Isabelle, pointing to the cover of Full Metal Alchemist as he returned to his room, her eyes deeply speculative and yet still beautiful.

Simon plucked the comic book from her hands, a coy smile slowly forming. "First of all, that is a boy. And second, I don't really care for blondes."

"They all look the same to me," she huffed before pushing the rest of the manga-inspired books back into their respective piles. "So, when are the love birds getting back?"

Jordan and Maia hadn't been around for days; Simon thought that they were probably off making out somewhere in a dark alley, or parading around in wolf form and howling together at the full moon. In either case, he was grateful for their absence tonight. "Who knows." Simon shrugged. "I don't keep tabs on them. Now, where were we?"

"I believe it was your turn," she answered, her gleaming onyx eyes like two giant saucers. He was immediately drawn in.

"Uh, yeah." Simon looked down to the deck of cards spread out on the bed. "Go fish."

"Really? After all that 'I've gotta go to the bathroom' nonsense, you're not even going to play a card?" she laughed, tossing her black hair over her shoulder.

"I did have to go to the bathroom," he scoffed.

So he'd gone in there to steady his nerves. What was the big deal? It wasn't his fault that he couldn't make a move—not only with the cards, but with Isabelle as well. Simon always wanted to touch Isabelle, to feel her smooth skin melting against his. He just didn't have the courage to take their on-again-off-again relationship to the next level. What if Isabelle didn't feel the same way?

"Please, you don't even have a bladder anymore," she sneered, though with the single lamp beaming down upon her face, Simon thought she looked more like an angel than Raziel himself.

"Don't test me when I'm hungry, Lightwood," he playfully argued. "Just play your hand."

"Do you have any eight's?" Isabelle stuck out her tongue.

Simon's stomach rumbled and he hoped that Isabelle couldn't hear it. She smelled so good right now—like blood and flowers. It tickled his throat, just as it had done when they'd raced through the park an hour ago. Simon cursed himself again for not finishing his meal.

"Nope, go fish," replied Simon as he tried to subdue the haunting reminder of Isabelle's blood, and the way that his body craved just one more taste, just one more lick.

Isabelle pouted and took another card from the deck. "You're no fun," she hissed, but the hint of a smile was enough to make Simon feel as though his heart could beat again.

"Hey, now, don't be a sore loser," he chided back.

"I'm not a sore anything. It's not my fault that the deck is rigged," she accused.

Simon threw his cards down; they tumbled to the floor just as Isabelle's head snapped up. "You saying I'm cheating, Izzy?" he probed, a smirk playing at the corners of his mouth.

"What if I am?" Isabelle leaned toward him. The smell of her blood taunted Simon as she grew nearer and poked at his chest. "What are you going to do about, Lewis?"

There were a million ideas forming inside of head, but only one called to him, only one seemed logical. He wasted no time before cradling Isabelle's face and bringing his lips down hard upon hers.

Instantly, the taste of wildflowers exploded in his mouth. He loved how soft her lips moved against his, and how each stroke of her hair felt like he was petting pure silk. She pushed him back against the crumpled bed sheets, her eyes like two pools of obsidian as she towered above him. "Wait, Izzy," he whispered, feeling that shred of doubt nagging away at his insides.

"Bite me," she pled. "I always love it when you bite me."

Simon knew from their past experiences that Isabelle actually loved the sensation. And Simon was hungry after all. "Are you sure?" he asked, wondering what pleasure might come of this.

She pressed against him, her breasts brushing his t-shirt. Her skin—warm, smooth, and intoxicating—flooded his body with more arousal than Simon had thought possible. "More than sure," she nodded.

He felt the throb of her pulse and the snap of his fangs as they came flying out, ready for a taste. Isabelle straddled him and lowered her neck to within inches of the sharp points. Simon wanted to latch on and drink until his belly was full and sloshy, to fill himself with Isabelle's essence. His fangs ached for that moment. "You're not scared?" he quietly inquired.

"Not anymore. Please, Simon," she begged. "Please…bite me."

He tasted rust and salt on his tongue from where his fangs had pricked the inside of his lips. But it was merely an appetizer; the main course lingered within his reach. "Yes, ma'am," he smiled, lunging up and slicing through Isabelle's skin as if it was made of nothing more than tissue paper.

Simon groaned as his fangs penetrated her vein and the blood flowed freely into his greedy mouth. There was nothing that compared to the taste of Isabelle's blood—not Jace, not Maureen, and certainly not Sebastian. It was like biting into pure Heaven.

She fell against his chest and purred like a kitten; her hands quickly found their way into his hair and began tugging on the locks with every urgent draw from his lips. Heat poured from her body into his, landing in all the right spots that drove Simon to the brink of insanity. This blood—Isabelle's blood—was beyond succulent, beyond the taste of anything he'd ever encountered.

With his belly full, he reluctantly broke away for her sake, immediately met by Isabelle's mouth as she secured him to the bed. "Wait, what are you doing," he uttered between forceful kisses. They'd never taken things any further than this. Did Isabelle want more?

"What I should have done that night in Magnus's apartment. I want you, Simon. I always have," she whispered against his lips.

God, he wanted her too. He wanted her so badly that his fangs refused to recede and the stirring beneath his jeans twitched in anticipation. "I want you too," he confessed. "But are you sure?"

"I have never been more sure of anything in my entire life. Who knows what tomorrow will bring," she answered, silencing his words with a strong squeeze of her thighs, and the feel of her skilled fingers delicately peeling off his clothes.

Simon pleasantly shuddered.

"One last hoorah before the world burns down," said Simon as he glanced up to the only girl that could ever purge Clary from his dead heart.

"If we only have tonight, then we had better make it count," she smiled back, stripping off the short, black dress.

If Simon thought that Isabelle was beautiful enough fully dressed, he had another thought coming. Her creamy skin was luminescent in the artificial light, gleaming with hundreds of scars that just made her that more attractive. He trailed a finger over one particular scar on her left arm. "That's for protection, isn't it?" he asked, feeling the edges fit together like a puzzle piece.

"You're my protection now," she cooed, pressing their naked bodies together as she leaned back down against his chest.

Her pert nipples rubbed against him; Simon felt himself harden to his fullest. He'd never felt as strong and yet as vulnerable in his entire life. Isabelle Lightwood consumed him on every level a man could be consumed. Especially if that man was a vampire.

Her blood coursed through him like fire, sparking subdued instincts that Simon had yet to uncover. His fangs jabbed at his lower lip again and in an effort to satiate their lust, Simon inched forward, licking the fresh, crimson streaks from Isabelle's neck. She groaned and arched her back, giving him clear access to her vein. But Simon knew if he took another lick of that substance, he would never let Isabelle Lightwood out of his bed again. Instead, Simon raised her hips ever so slightly, and followed suit with a slow, careful thrust of his own.

As new as he was to this whole sex thing—not to mention the lack of knowledge regarding a vampire's capability to reproduce, though it was thought to be impossible—he craved Isabelle's body just as he pined for her blood. The very same blood that was swirling around the room, and filling his senses with the reminder of Isabelle's flesh, her flavor, her power.

The taste of Isabelle devoured him whole.

She lowered herself onto his length, taking him in deeper and deeper with every needy stroke. Simon's toes curled, his eyes rolling back as he allowed his temptress to guide what might be their last evening together for a very long time…maybe even forever. She was right—if they were destined to watch the world burn, then they should have a little fun before that sentence was carried out.

Simon's outstretched fingers played around her breasts, squeezing gently upon her command. He was new to all of this, but it was definitely apparent that Isabelle was a well-seasoned pro. She knew exactly how to bend her body, and how to pull a whimper from his quivering lips with the lightest of touches.

"Don't stop," he grunted as Isabelle quickened her pace.

She grinned down at him, those dark eyes full of desire and desperation. He'd never seen anything as seductive and inviting as this. Hearing Magnus speak of sex like it had taken centuries to master every tantric art, Simon had thought that his first time would have been awkward and rushed. But Magnus had forgotten to mention about a vampire's natural ability to keep pace with whatever circumstances were thrown in their direction. Simon's body reacted to Isabelle like it had a mind of its own.

"By the angel!" Isabelle cried out as Simon grasped her hips and regained control.

"Am…I…hurting you?" he panted, fearing that his hasty thrusts might be causing her pain.

"Quite the contrary, tiger," she winked down at him, her breasts bouncing faster and faster as Simon's hardness slammed into her body.

"Rawr!" he chuckled, his fangs popping out again.

He heard the corniness in his own voice before Isabelle let out a disgruntled sigh. "Okay, nerd boy, that's enough…of that…" she trailed off, losing her voice to the pleasure.

The momentary comedy was over, and despite the erotic rush of desire coursing through him, Simon agonizingly forced the two pointed needles back into their respective holding place and bucked up into Isabelle.

Suddenly, they were sideways, Isabelle caving to the immense strength that they were both pouring into this single act of ecstasy. Simon carefully rolled them over; Isabelle's soft hair spread out on the sheets like a waterfall of black ink. He placed his hands on the pillow, directly on either side of her face, continuing the gentle, yet urgent, pumps. "You're so beautiful," he crooned. "Don't ever let anyone tell you differently."

"I…" she trailed off again. He longed for the day when Isabelle would complete that sentence. It was the second time he'd believed that she was about to say "I love you". But he would wait until Isabelle was ready to admit how she felt, how he hoped she really felt.

"You don't have to…s-say anything," groaned Simon, his voice breaking.

Her fingers twisted into his hair, bringing Simon flush against her lips. With a mammoth growl that practically rivaled his own, Isabelle released around his cock, rocking his body with vibrations that he'd only read about in magazines. The spasms were so intense that Simon couldn't handle it, his stamina crashing to a halt as he spilled into her like a shooting geyser.

"Simon…" she purred lightly in his ear, the rest of her words lost on him.

All he managed to grunt out was, "Izzy," before he collapsed onto the bed next to her heaving body. In the glow of the light, her sweat-laced skin glistened like thousands of tiny jewels. Simon reached over and gently brushed his fingertips down her trim waist. She smelled divine, like blood and flowers and sunshine.

"Well, I guess this changes things," Isabelle quietly said as she cuddled up beside him.

Simon draped his arm around her, finding that his stamina was quickly building again. "It doesn't have to…if you don't want it t-to, t-that is," he stuttered, even though he prayed to whatever God would have him that she wanted to continue on with their relationship.

"Oh, no, Daylighter, you and I are in this together," she laughed, giving him a peck on the cheek.

"Until the world burns down." He tugged the blanket around them.

Isabelle nodded against his shoulder. "Until the world burns down."

.