Dude gives off NTR antagonist vibes lol but he doesn't really do anything too bad. This is probably the closest the "let me train you to be sexier to appeal to the other guy" spiel ever came to making sense because Oh-chan really DID go for the other girl entirely because of sex appeal.
Honestly I couldn't figure out the continuity of this series if I took a college course on it but this one's the first one so that doesn't matter here. The important thing is that this is a really hot book about some dude's chick getting absolutely fucking wrecked and losing to the cock. The best part of these types of stories is seeing a girl throw away all sense of reason for the sake of lust despite being treated like a cumdump and Miito Shido really knows how to deliver that.
Kind of interesting how this twists the childhood friend trope. Many stories portray the childhood friend as basically the only guy in a girl's life, like their boyfriend by default. But people have other relationships too, and the childhood friend relationship doesn't exist in an inviolate bubble that doesn't interact with other relationships. Aside from the indecision angle, it's also interesting how the other guy reacts. Yeah he's worryingly insecure, and a douche, but it is a situation with a lot of potential for suspicion and jealousy right? Like now that you've given childhood friend-kun the wakeup call, what if he does try to make a move? He's clearly still got feelings for her.
I love Takashi regardless because I do like his art and story telling, but if Takashi drew a fully consensual gangbang with a big titty chick like Hiromi I'd nut so hard I'd blast a hole in the ISS.
The way he suddenly proclaims an epiphany at the moment she's about to dump him is a huge red flag too...it's very insincere. Honestly I was expecting the ending to be that he knocked her up and now they're stuck with each other as outcasts.
But I like the ambiguity...it feels very real, because in real life there's no inner monologue to tell us that he's a self interested scumbag without a doubt. We could only watch his actions and the words he says, and infer for ourselves his character from the front he shows us.