I'm not certain that this deserves to be considered a "good" fic, for what it's worth, but I'd certainly list it as "required reading".
Spelling and grammar seem solid enough, the pacing goes at a nice clip. The flow of events in that final chapter feel a little "off" (a bit rushed, contrived, and TEH DRAMA), but certainly an acceptable work overall.
Obviously, there's a heavy bit of deliberate out of character, etc., but no one should have been expecting much fidelity, given the tone and plot.
And of course there's the factual standpoint, that you can't go into debt from illness in Japan because prescription drugs come in vending machines at 500 yen or a 30-day supply, and they actually pay you to stay in their hospitals, but it's reasonable to expect that most Americans don't know that.
The setting is silly fun, and that's all well and good. What really makes this fic shine, in my opinion, are the one-liners:
Nomiya wasn't really a dirty old man, but a big old softy who enjoyed pampering young girls. For some reason, his last two wives didn't think it was such a harmless hobby.
"Roses are red,
Violets are blue,
Better have Lilly's money
Or she'll fucking kill you."
"You a cop?"
"Oh. Well, even if you were, not like you'd tell me anyway, huh? Get in."
Kenji did everything manly, even girly drinks.
You kind've look like a whor- erm, what I mean to say is that subtle, natural colors would look better on you.
And so on.
Also, interesting the convention of giving Hisao two "selves" and remaining consistent throughout any given chapter.
In short, it would've been really easy to just phone something ridiculous in for a few lols and move on. Instead, there's a surprising degree of care put into the craft.
A shitpost of this caliber deserves to be displayed in a museum. (Too much? Yeah, I think so too.)