I mean I might be remembering incorrectly but the seme in "again" wasn't a red flag. Or was he?
Mentally unstable but trying to do better
https://www.mangago.zone/read-manga/the_world_without_you/
Master × commoner
https://www.mangago.zone/read-manga/a_proxy_painter/
Isekai to atone for his sins
https://www.mangago.zone/read-manga/palace_of_bardo/
This one doesn't exactly become green flag, he's now just a red flag with a little bit of emotion haha
https://www.mangago.zone/read-manga/love_history_caused_by_willful_negligence/
Psycho in therapy lol
https://www.mangago.zone/read-manga/mary_jane/
R*pist motherfucker into puppy dog seme
https://www.mangago.zone/read-manga/beware_of_the_full_moon_in_march/
Demon into daddy demon
https://www.mangago.zone/read-manga/night_song_mgs/
Homophobic brat to NOT GAY BUT I LOVE YOU
https://www.mangago.zone/read-manga/crossing_the_line_1/
P.s: I personally don't think some of these guys should be forgiven, but it's the trope you asked for
someone please recommend me red flag to green flag (seme or uke but preferably semes cause most of these mfs are shit) stories where they treat their partner like shit but then suffer from charachter development please please please. specifically trope like time travel, reincarnation, anything similar to that just gimme!!!! currently craving for redemption arcs.
I've read
Again
currently reading
Beyond memories
You own my all