Saimin Gakuen 2-nensei

The protagonist is a student of a third rate university with an awkward personality and sullen looks. His interests are deviant as well, but as an adult he has no shame about this. He acts like a stalker, and sneakily digs through the trash in the middle of the night. Naturally he's avoided by everyone around him.

At one point, he picked something like a toy gun out of the trash. Wondering if it might not have some monetary value he began to fiddle with it, and unexpectedly it became clear it was a device for inducing hypnosis.

Then, knowing it would normally be entirely impossible, using that device he became a student teacher in an all-girls school. Through this, the protagonist set about satisfying his own desires to his heart's content.

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Following the events of the first game, the protagonist lays his poisonous fangs primarly on the new heroines, which are second year students. The heroines of the previous game and the main heroines of the next game play a big role as well.