"Sizzy First Fight?" -Anonymous via Tumblr

A/N: I didn't know what to make them fight about so I sought of just went with it. Please leave prompts in the reviews or ask me on Tumblr at officiallyobsessedblog. -Izzy

Set after City of Heavenly Fire

Clary couldn't sleep. Neither could Jace for that matter, and the two of them lay side by side, in their shared bed in The Institute with their eyes wide open as they listened to the shouting match going on a few doors down. She wasn't entirely sure how it started, she was kind of busy at the time.

She had gone with Jace, Isabelle and Simon to catch a demon that had been reported by one of their allies. No big deal, she had gone out on loads of similar battles with Alec, Jace and Izzy. But this was one of Simon's first times as a Shadowhunter.

Unfortunately, he had made the mistake of underestimating Isabelle Lightwood, which was much more dangerous than any demon out there. Simon's heart was always in the right place, but sometimes, he could be a romantic at the most inopportune times.

He didn't realise that Jace and Isabelle had devised many strategies years before hand. All Simon saw was a demon that was about to attack Isabelle from behind, so naturally he pushed Izzy out of the way, which foiled her plan with Jace. Not only did Simon almost get himself killed, but it almost cost Jace his leg.

This was from what Clary could gather from the argument, anyway. She didn't actually see it happen, she was focusing on one of her own demons.

"You're new at this," she heard Isabelle yell down the corridor. "So you need to learn fast that if you give me your complete trust and cooperation, things will run much smoother!"

"She has a point," Jace nodded.

Clary was pretty sure he was going to side completely with Isabelle, since she was technically his sister, but he seemed to be listening to Simon's side of the argument, and he seemed pretty unbiased. "Yeah, but so does Simon," Clary said.

She listened as Simon tried to say something, but was cut off by Isabelle. "You do this all the time! You never trust me."

"Lie," Clary muttered, knowing the way Simon felt about her.

"I trust you with my life, okay?" he exclaimed

"Truth," Clary nodded, satisfied that he set the record straight.

"But you don't trust me with my own?" Isabelle demanded.

Jace sat up and pointed at the wall. "Another point for Iz," he said. Clary rolled her eyes as sat up, continuing to listen through the walls as Simon tried to come up with an answer. "Is it bad that we're eavesdropping?"

Clary shrugged. "Nah. I don't think they've ever really fought like this before."

"They've fought," Jace said.

"They've bickered," Clary corrected. "There's a difference. This is like, a real fight. Not a break-up fight, but still a real fight."

Isabelle's room was only two doors down and Simon was aware that Clary and Jace could probably hear everything that was going on. But at that moment, he didn't care. He didn't like arguing with people he loved, especially Isabelle. He hated it, and he kept looking else where, or doing something with his hands to try and take his mind off of it, despite that fact that Isabelle was perfectly comfortable yelling at him.

"For the Angel's sake, Izzy," he said, not entirely sure if he used that phrase right. "I tried to protect you, but I failed and I'm sorry! Why must you pick fights about the littlest things?"

"Littlest things?" Isabelle demanded. "You could've died, Simon! I can handle myself, but you almost died tonight, all because you didn't trust me! And not only did you put your own life in jeopardy, you almost cost Jace his leg. You can put your own life at risk all you want, but the second you hurt my brother I will tear you apart."

"I didn't intend to hurt him!" Simon exclaimed. "I don't know if you've noticed, but he's still got both legs!"

"Thanks to his own quick thinking," Isabelle growled, her arms crossed as she glared daggers at him. "You have no idea how lucky you are." And Simon believed her. He honestly believed that if Jace had just been a little bit slower, if Jace had actually been injured, he wouldn't be that at that moment.

"This isn't my fault!" he told her, throwing his arms up in anger. She tried to say something but he interrupted her before she could start. "No, Izzy, this is you being a control freak! You need control of everything and you can't even admit it!"

Isabelle paused for a second, not out of shock but out of anger. Simon resisted every urge to back away slowly.

"I'm the control freak?" she asked, dangerously calm. "All you did tonight was try to control me. Don't start again on that protection bullshit, I can take care of myself. I have been doing this my entire life."

This time Simon paused, taking a deep breath to calm himself as he tried to think of the right thing to say.

"Well I haven't," he said. "I'm completely new at this and I'm not talking about demon hunting." She narrowed her eyes. "I've never been in love before, Izzy. Surprisingly enough, this is my first time. So I'm sorry if I make mistakes or slip up. I don't mean to, and I'm trying."

She sucked her teeth, looking slightly less murderous, but still thoroughly pissed off. "Just get out," she muttered. He made no effort to move. "Go on!" she yelled. "Get out! Now!"

Clary and Jace heard something smash and the sound of Isabelle's door close. They turned to each other. "I'll go and talk to Simon," Clary said. "You comfort Isabelle."

"If, by comfort," Jace said, "you mean string up a punching bag and find a picture of Simon, then sure!"

And that's how, at 2am, Clary and Jace had to get out of bed to solve the problems of another couple.