Kôkô kyôshi: Kuroi shitagi onugu toki (1997)

Synopsis

World history teacher Kana has another side to her. She wears red lipstick and black underwear, and is the face of a woman who calls the two-shot dial as usual, seeking a man. One night, she is spotted by her student Shinji entering a hotel with a man. Shinji, who was in love with Kana, follows her around during class, lunch breaks, and even after school. Then her former lover shows up to press for reconciliation. Before long, Kana even begins to feel anxious when Shinji is not around.