There's a lot of hinkey stuff in Murakami that I somehow didn't register when I read it in English back in 2011 but that necessarily impresses itself when reading more slowly in Japanese. While slowly reading polite Japanese, which is  like hacking one's way through an overgrown garden, cutting out all the excess verbiage and causative forms and verbs of giving to get at what's being said. (Polite Japanese, not prewar keigo, thank god, because that's like hacking through a jungle.) But there's one clanging 'oh no they didn't' moment that's really... guy, do your research.

Woman teacher is on a school outing, suddenly gets her period ten days before she should, sends kids off to look for mushrooms in the woods and takes herself deep into the forest to mop up with the handkerchiefs she has, because you always have handkerchiefs in Japan to dry your hands. Towels not provided in public washooms. Then she hides the bloody handkerchiefs where no one will find them and goes back to the group, still bleeding into her underwear, presumably.

No she doesn't let go of those handkerchiefs. She keeps them stuffed in her underwear because seriously, Haruki, periods aren't a single effusion of blood that then stops. Don't you know any women at all?

You need bloody handkerchiefs for a plot point? Find something else then. Mattaku.