According to news and court records, Daten Sakusen author Yamamoto Shouichi was a high school art teacher at the time (2016), he and the 15yo female student got close in school and started kissing her in the car. When she became 16, they went to hotels and had sex. It went on for 3 years, once or twice each month. He was 30 years older than her. But that's not the most horrible part.
From the court records, the things he did to the student included: scatology, taking photos during sex, outdoor nude photography, outdoor sex, writing insults like slave on her body, using sex toys on her in public, enema, causing her ptsd. The court ruled on 2026/2/20, he must pay her 11 million yen as compensation.