Wow, look; another MC who decides he is still in Japan, the whole world works like Japan, and is terrified of the sight of tits.
I'm shocked.
See? Here's my shocked face: 😐
So shocked.
You should have him shriek at the top of his lungs every time somebody says "sex," just so the reader can be further confused by the ridiculously utter nonsense.
I've known lots of Japanese guys, by the way; none of them were terrified of boobs, nor did they shriek at the tops of their lungs while sprinting in circles like a border collie at the sight of breasticles.
Actually, they acted just like every other bi and straight human male I've ever known from every country when presented with the sight of boobies: they stared. Sometiems uncomfortably, sometimes in admiration, but they didnt shriek, they didn't yell, and they plainly didn't have a problem with it.
I find 15 to be emotionally and mentally too young for such things, but maybe they have 2 extra months in their years, or maybe they live shorter lives; we dont know (yet).
But if that's the age of an "adult," it isn't that much different from 14 (Germany), 15 (France), 16 (Japan and UK), or the different states in the USA... just on the west coast of the USA, Idaho is 14, Washington is 16, but Oregon and California are both 18!
So, really... 15 is just a personal preference; for me, it's WAY, WAY too young!
[EDIT: it's "way too young" for me because I'm old; in my teens and early 20s, that'd been a different story]
But it's not weird, and this MC is being a collosal dipshit in a LOT of ways...