Basically it’s a girl who all her life has looked and has been treated like a boy, and she finds a cross dressing guy who’s always wanted to be a girl and they kind of start a relationship? There’s also another girl who has black hair and straight bangs, who is in love with the tomboy ands she’s like a small cute girl. The manga basically focuses on gender and it’s explicit. If I’m being to vague let me know!
Maybe it’s ‘Kanojo ni naritai kimi to boku’? https://www.mangago.zone/read-manga/kanojo_ni_naritai_kimi_to_boku/
The FL gets a boyfriend and then he dies idr how but she goes to her room and he’s like a ghost and so they try to figure out how to make him rest peacefully. The ghost bf sometimes turns evil and his hair grows and his pupils turn dark. I know that it has a Japanese show adaptation too.