Well it's a work written by a Japanese author to a Japanese public. It's target to them, and they like this trope so....
Wish i could like your comment, this one for you
It wasn't really brainwashed tho, didn't feel like Stockholm syndrome either which I actually liked about it.
The rape wasn't as bad as I feared as well, usually it's less consensual(?).
I know it wasn't completely but I'm used to worse I guess.
Also I think it's considered normal to fuck around in their circle of people, at least that's what's shown in this manga.
Even the Uke grows accustomed to it and the girls don't even mind, that aspect felt very open minded to me.
Yet again I agree that it was a rough start and I didn't enjoy the first chapter much myself.
I can't say I really liked this, once again its just how ever yaoi basically starts with a rape trope, like ppl its 2021, gay is a thing. If a guy wants another guy he doesn't have to rape and brainwash him into liking it, he just has to flirt. But Im just here for the smut nowadays (〜￣△￣)〜