Enchanting Temptation On The Outer Limit summary:

One night, Mr. Kano, a high school teacher, was led by children wearing peculiar masks to a shop run by a strange man. “Do you have anything that you’ve lost… that changed your life?” Mr. Kano begins to tell the story of his sultry love affair with his student, Itaru Enatsu… Students and teachers, step-brothers… In a world on the border of this world and the next, what will they choose? Love? Or illusion? The curtain raises on Nobita Akiharu’s beautiful world, a boy’s love omnibus!