Bibi is still one-of-a-kind. However, but if you are looking for characters with dark/problematic personalities, maybe the following will be interesting. Second, third and fourth ones contain smut:
- https://www.mangago.me/read-manga/camouflage/
- https://www.mangago.me/read-manga/love_thy_neighbor_2/
- https://www.mangago.me/read-manga/white_angels_have_no_rest/ (this one is a bit too problematic so don't proceed if you feel uncomfortable)
- https://www.mangago.me/read-manga/i_reincarnated_as_the_little_sister_of_a_death_game_manga_s_murder_mastermind_and_failed/
Anything like I Love Amy? https://www.mangago.me/read-manga/i_love_amy/