Side character stories are so fun, sometimes I wish they could be elaborated into novels of their own, but I can also see that the reason they can be good is bc they're so simplified. Some subplots on side characters ive read from different novels ML's subordinate sleeps with mysterious woman, his hated male coworker/rival suddenly quits work and flees, later he finds a woman that looks like the co worker and it turns out coworker is A) female B) has a child that looks like him. FL's BFF marries ML's Ex friend to prevent FL getting sued for fraud claims. FL's assassin friend seduces the older brother of a man she killed. Later a rival assassin kills off that mans entire family and tells him the friend did it, she admits to killing his brother but denies killing his family but he doesn't believe her and tries to kill her (he's unable as she is too skilled). She dies protecting him and he becomes a monk. FL's scummy husband (not the male lead) has a friend who gets drugged up with aphrodisiacs in a scheme to hurt the FL, she throws him to the ML (a rebel on the outside)'s assigned shadow guard, and the guard decides the best solution is to bed the dude instead of killing him lol. unexpected bL in hetero novel. Alternate universe in a quick transmigration novel where a second male lead DOES get the girl and the original male lead don't exist in that world. I can't think of more atm but there is more im sure.
I prefer stories that give relevance to side characters instead of just making them all in awe of ML/FL 24/7