i think its mainly because well, they are serial killers and in ronin's "good" end SPOILER kinda: (angel said she would kill the mc for killing ronin.) so i would assume they would all kill for the mc, at least if they asked and they were in a relationship. and i think its fair to say that that leans more on yandere territory, also ronin is honestly a bit (a lot) crazy so im surprised you didn't get yandere vibes from him. especially when he said he wanted the mc to 'prove themself by killing someone for him' (the part i want to really highlight is the 'for him') but ig you could just say that he said that to prove them wrong but when i said i would, he blushed and really seemed like he enjoyed hearing that. also, if you played to get ronin's """bad""" end, im even more surprised because it gives major yandere vibes. because again. he is crazy.