Is yashiro here a power bottom? Y'know like the one in charge of sex?

Not really

his character is dominant yes but in the bed he is not the type to likes dominate but rather prefers getting handled roughly, other one use him like toy and made him submit since he is masochist. but this is coming from the trauma of getting raped in childhood from his father so we can’t say this is his actual liking. in fact, quite the opposite is true; Doumeki doesn't use him like the others, he's even affectionate and tender with him when they're sleeping together, and although he secretly yearn this obviously, he’s also afraid of this unusual comforting feeling, and that's one of the reasons he pushes Doumeki away as well