Emilia

Cain's younger sister

Doesn't respect him in the slightest because she had to take over all his responsibilities as the family heir when he ran away from home 

Comes off as a little arrogant but she's just lonely and doesn't know how to talk about her feelings............. :-/

Has a seemingly incurable disease that makes her physically weak so her parents made Fedja research ways to cure her

Has never really been able to go out so she has no friends (Despite desperately wanting them) 

Fedja is also the only one she can talk to since her parents, brother and servants don't care much about her as a person 🙂 

They bond over being depressed, not being able to go outside and hating Cain