The menstrual cycle isn't the most likely topic for a commercial film. In fact, Shunsuke Shinada's "Little Miss Period" is the first I know to address it.
The inspiration is a comic by Ken Koyama that, after debuting in a web magazine in 2017, quickly became popular with women (who were evidently OK with its creator being a man). It is currently appearing in Comic Beam, a monthly magazine aimed at teenagers. So the progression to film is not totally surprising, given the vast number of manga-based movies made here.
As the title hints, the film combines quirky fantasy and quotidian reality to funny, heart-warming and instructive (at least to male viewers) effect. The structure is episodic — reflecting the comic's standalone-story format — and the plot lines are predictable, but the firmly grounded performances of leads Sairi Ito and Fumi Nikaido help steer their stories away from the cartoony and the treacly, the Scylla and Charybdis of so many manga-based movies.