If you loved High School Teacher: Maturing, try Flower and Snake 4: White Uniform Rope Slave
A bridge between a film you've already seen and one most people haven't. Here's what they share, and what the second one does that the first one doesn't.
You already loved

High School Teacher: Maturing
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Flower and Snake 4: White Uniform Rope Slave
What they share
Both films are directed by Shōgorō Nishimura, and they sit in Drama territory. If that's the register that drew you to High School Teacher: Maturing, the second film will land in a comparable space — through a different lens.
What Flower and Snake 4: White Uniform Rope Slave is
Operating room. Hum of the drill. A dentist and his nurse find ways to monetize their patients' vulnerability. He develops a fixation on two new clients, unaware of the women's own games. Nishimura's erotic thrillers are not for all tastes.