Eren : He loves it when ever you are really into something you tend to bit your lip. You don't know this but it drives him crazy ;)
Levi : He would never admit this to you, but he finds it adorable when you scowl other people for not doing something right , it makes him proud.
Erwin : He finds it cute whenever you guys are fighting titans or just a simple sparring match , you always tend to get worried for him. He loves it because it shows that you care for him.
Armin : He loves the way you always read with him or listen to him when you guys are talking about something. Some people might think that reading books is boring so they would always decline, but when it has to do with you, you would gladly accept the offer. He finds that extremely adorable
Jean : Jean finds a lot of things about you cute , but what really makes you attractive is your cheeky and humorous personality. He feels like he can actually be himself with you knowing that you won't judge him.