Jace
His training. It's kinda shallow but its still appealing to see. Since he is a shadowhunter he trains daily but normally at the institute. Recently he moved in so you turned your spare room into a sorta training room.
Jace doesn't like to be confined so normally only wears sweatpants to train. He gets all sweaty and looks rugged as hell which turns you on.
He found this out at one point and made sure you were always aware when he was training. You didn't complain.
Clary
Her drawing. She gets so focused when she's drawing and you love it. She will bite her lips, furrow her brows, glance around the room, keep touching her hair and to you, it's hot. You don't know why though.
When she draws you it's even worse. Her constant looks added to her drawing habits is amazing for you. Often times you begin to get fidgety which causes her to scold you.
You try to sit through her drawing but often time she doesn't get to finish. Well, at least the drawing.
Alec
Him with motorbikes. Not many people realise Alec loves motorbikes (it's in the books but you can apply it to the show). He gets so excited to see them so for his birthday after he moved in with you, you gave him a motorbike.
It was kinda run down so he had to fix it up. A lot of the time you'd come home to see him working on it. The bike made him oily so he often didn't wear a shirt. And it was still hot when he did. Normally you would stand and watch him for a bit until he noticed you.
Alec would put down what he was using on the bike and walk over to you. Izzy had found out you found it hot so told Alec. This caused him to have a smirk on his face as he walked up to you. He would walk closer and closer till you were pressed up against the wall. He'd gently grab your jaw and whisper in your ear "we cant ride the bike yet but theirs something else you can ride."
(GET ME SOME HOLY WATER...nvm it would kill me)
Magnus
Him doing magic. Magnus often practised magic casually. Trying random spells and such, though that's not what turned you on. Well sometimes.
Once every so often Magnus would like to try some more complex and stronger magic. His hands and fingers moved in ways that made you shudder and his face was so concentrated and hot. Depending on the magic he would get really hot and sweaty so wouldn't wear a shirt.
You would pretend to be reading on the couch but really watch him. When he would notice he would drag on the sessions with a teasing smirk. As soon as he was done, or sometimes before, you would grab him and pull him in for a deep kiss. "Bed. Now."
Izzy
When she changes in front of you. Izzy's confident in her body and doesn't give changes in front of you a second thought. She would have to change for missions but she also wanted to spend time with you.
This normally meant you would talk with her casually while she changed, her changing and you on the bed. She was so hot but you didn't say anything as she had a mission. However, once she got back you were quick to greet her.
Other times if she wasn't rushing somewhere if she changed in front of you she didn't always finish getting changed.