Curate, connect, and discover
something that caught my attention while rereading though they drift, they do not sink, but nor do they sing is that yashiro never refers to his stepfather as, well, his stepfather. neither out loud when he tells kageyama about the abuse, nor in his thoughts. he calls him his mother's husband instead (再結婚相手, so second marriage partner if you want to be literal), which is interesting, right? there's this refusal to draw a direct familial connection, he's just a man yashiro's mother married. that's all there is to it.
it's different with doumeki, though. when yashiro tells him about the abuse, he calls the man simply his father (父親) at first, then notices this... slip up, almost? and specifies - stepfather. whether it's because yashiro accepted that it wasn't just some man who had nothing to do with him, but rather a parent, someone who's supposed to be caring and protective, or because the little pretend game of familial connections in the yakuza made the word "father" so inescapable that there's no point in avoiding it anymore, i don't know. probably both.
it's important that yashiro opened up to doumeki specifically, too. every other instance where he thinks or talks about his abuse, both with aoi and misumi, he doesn't reference his stepfather at all. it's just this vague "when i was a kid i was violated by a man. that's all". there's no clear timeframe and no way to even tell if he's referring to a specific man or not (as in, no clear distinction whether "man" is singular or plural). it feels almost impersonal. the only people who get to learn the truth, in yashiro's usual dismissive tone, but with enough details to make it something that they have to look at, are the man yashiro was in love with and someone reminiscent of him. neither kageyama nor doumeki know what to do with it, though.