Thank God it wasn't the eldest. There's too many student/teacher illegal ass trope. I reread so I already knew the ending but the eldest one had such a gross personality (literally was a hair of irrationality away from raping Yui just out of pettiness) as well as the 2nd brother and Yui just letting himself be groped like that for no reason... bruh. It's Hella weird considering he as a child literally put a boundary within himself to not feel too attached to ppl in new York since he was gonna leave them in the end... why the hell would he be that oblivious to being groped, especially if it was like doh slobber in his mind coming from a HUMAN??? Like bruh get a grip. The whole dog thing just seemed like a cop out for what was probably a freeze response that he didn't know what a freeze response actually is and reflected on a "similar" enough experience to explain why he didn't react. No one ever remembers there's not just fight or flight. It's completely normal if someone freezes out of shock/not fully accepting reality of what occurred in the moment fast enough. HOWEVER, while in later grope attempts to him he manages to voice in some way he doesn't care for it, he never firmly sets a boundary and just endures it instead. And the damn 2nd brother only doing it because he's actually in love with his OWN brother. Ugh.
but I'm glad it's Hotaka.