The group sex scene honestly felt like such a backslide for Ueno. The whole "developed"/"groomed" aspect has a thick layer of Japanese representation of mental health, like, fetishism (in a DSM-V medical sense) can be a real issue for people and I really liked how they portrayed it as a problem for pretty much everyone to different extents. But then they leaned into the "developing" so much as if they're inflicting fetish D/S play into each others psyche. Like, finding someone who gets your kind of freak is nice and fine (and with coming of age stories, it being through messy situations is pretty par for the course). Idk, it feels silly to try to pin down exactly how this ended rubs me the wrong way considering the vibe the manga as a whole has (watch a kid come to terms with sexuality and self actualization through the molestation), but it feels like the bad-ending but framed as a happy-ending with a pretty unhealthy perspective of kink. Like, the whole time Ueno struggles with denying his kinks and trying to change himself, and through standing up for himself, he is kinda coerced into giving up in favor of fetish acceleration. Sure, they gave vanilla a try, and going to a couples sex therapist and talking their way to an understanding doesnt make for a good story, but a big reverse gangbang to rid him of guilt/shame felt like a real flatline. Maybe I should've read this for the sex instead of the plot, have my favorite waifu, grab some popcorn and tissues, but unlike most horny manga, the plot had a MC genuinely struggling rather than just pure fantasy.
Idk, I think ultimately the manga fumbled the landing of the story in favor of sticking the landing of the fan-service. And it fumbled moreso in the tone/presentation of the ending rather than the events, I'm not complaining about the cannon events, but the portrayal of the events, pretty much just from the group sex onward. Except, the stalker ex bf having a happy-ish post NTR ending did kinda suck imo, probably the most unnecessary way to end a plot-line.