A/N: Well, hello there! I've always been a fan of Sizzy and writing about their complicated relationship is always a fun challenge. If you have a prompt or a situation you'd like to read, don't hesitate to tell me and I'll see what I can do about it! I promise to give credit to whomever's prompt I'll be using.

Disclaimer: If I owned The Mortal Instruments, I wouldn't be writing this.

He wasn't her type; too gangly and too awkward.

Isabelle only ever dated men and Simon, unfortunately, was still too much of a boy. Actually, he was too much—vampire or not, period. She could list every reason why she shouldn't even go for him; he was still hung up on Clary, he was still in that ridiculous boy band of his, he was still very much addicted to that game—what was it, again? Oh yes, Dungeon and Dragons. As if real life with real dangers wasn't enough. And he was still too dense to realize that she, Isabelle Lightwood of the Shadowhunter's New York Institute, had taken an interest on him.

But. With all of her reasons accounted for, there was still something about him that fascinates her. Something that makes her stop and look further into him. Something that makes her convince herself she shouldn't do this—because if she did, she'd fall in too deep. And Isabelle Lightwood never falls in too deep.

She gritted her teeth to stop herself from tearing her hair out. She didn't know what that something was. Damn it. Why was she even acting like this? Damn him! And damn that smile on his face!

Wait.

That was it!

His smile. She hadn't seen someone smile that radiantly before. Like his smile can summon Angel Raziel out of the depths of Lake Lyn. Like his smile can leak sunlight from between his lips. Like his smile can make anyone fall in love with him.

Oh, by the Angel. What was happening to her?

"Iz? Are you okay?" Clary's soft voice broke into her reverie and she felt her hand poke her arm gently.

Isabelle turned away from the boy, who was far away to hear them talking, polluting her thoughts to smile at Clary, albeit confusedly. "Yes, Clary, why wouldn't I be?"

"Because you're looking at Simon like you want to murder him? Or eat him?"

She found herself snorting at her friend. "Why would I even want to eat Simon? He's—"

"He's what?" Clary's voice was surprisingly sharp as she cut her off and was looking at her hotly. If only she could raise an eyebrow, she'd look far more menacing.

"He's… well," Isabelle searched for the right words in her mind. She didn't want to offend Clary; she knew how protective she was of Simon. Sometimes that infuriated her but really, now's not the time to dwell on that because Clary's still glaring at her and Isabelle herself was starting to get pissed off. "Well, because he's a person, Clary! And I am not a cannibal!"

Clary blinked at her, not really expecting that kind of answer from Isabelle. She studied her friend carefully, from the way she was clenching her fists tightly to the way her eyes kept on going back to Simon. A few moments later she got it but decided to keep her mouth shut. Izzy was already unhinged as it is. Who knew Simon even had this effect on her?

"You're so weird today, Iz. What has gotten into you?" was all she ever said.

Isabelle didn't need Clary to tell her what she already knew. She ignored her rhetorical question and went back to cursing Simon in her head. She noticed he had stopped playing with Chairman Meow's upturned belly and was now approaching the couch she and Clary were occupying. He plopped down beside her rather ungracefully, making her glare at him.

He turned to her a second later and grinned.

Isabelle was a strong girl. She was one of the best Shadowhunters in her age. She was strong and impenetrable. But Simon's smile could easily make her weak in the knees and she found herself falling.

Damn it. She was so not looking at him again.

A/N: Meh. Not really proud of this but I've had this in my mind for a long time now. Might as well as write it down, right?