Why the hell did the author make her 17? Isn't she, like, a detective? I've been skimming for a while. The story wouldn't be any different if they had made her 19 or in her early 20s, no? Reminds of that one catgirl manga. I guess the author just wanted to invent a reason to drag out their relationship and chose the weirdest possible way?
And you just answered your own question. A story is driven by its conflict, and the conflict isn't always a matter of confronting external antagonistic forces. The conflict of "he wants to wait until she's old enough while she aggressively flirts with him" is also a valid (if frustrating for some) example. Helped by the fact that the one time he
did almost act on her advances, it was heavily implied she wasn't nearly as ready for it as she claimed she was. So he had to be the figurative
and literal adult in the relationship and restrain himself.
It's Japan. Unfortunately a non insignificant number of people (predominantly men) have an extremely thinly veiled fetish towards young women, and in some cases outright pedophilic inclinations within the demographic that consumes manga. It's why so many of the more ecchi/hentai stories are set in high school, and why lolita content is a thing.
There is an argument to be made that it's better to consume said content through fictional mediums, but considering Japan still has an issue with underage compensated dating and their highly questionable idol culture, it's not really what i'd call a convincing argument.
(Also not saying this isn't a problem in the rest of the world, it is, Japan is just seemingly more open about it)
Is it better or worse that Japan is open about this stuff...? Also, to my understanding "compensated dating" is just as often
literal dates; going out for food, going to movies, etc. It's more comparable to an escort service than prostitution. And unfortunately, underage escorts/prostitutes are
very much a thing in other countries, including if not especially the West. Since sex work is so heavily frowned upon, there's no means of regulation or protection.
The idol stuff I'd also blame on corporations rather than the people. These companies go out of their way to facilitate and encourage parasocial relationships with their idols so the fans will spend more money. Which, shocker, turns out to be horrible for the mental health of all
actually involved.
Ironically, while I'm very much of the "fiction should not be equated to reality" opinion and people should be allowed to enjoy whatever fictional content they enjoy, I
did hear a legitimate argument on the point when discussing the subject with a therapist. Namely that such "content" is a source of pleasure and stimulation, much like other stimulants (drugs, caffeine, alcohol, etc) and that if one isn't careful or capable of self-regulation, the pursuit of ever-increasing stimulation can escalate to dangerous and then illegal, devastatingly harmful levels. I am still of the opinion that fiction =/= reality and anyone who blurs that line is ultimately responsible for the consequences of their own actions, but it was refreshing to hear an argument with
actual logic behind it.