ストラッシュ

Strush is a 1991 PC-98 adventure game by Orange House that follows the story of Shinobu Aiba, a somewhat agreeable detective that's investigating why students from an elite high school have been disappearing. Enlisted by student council president Rika Izumi to look into the disappearances, Shinobu goes undercover at the school and navigates relationships, coverups, and scandals, all while a formidable woman from his past seems to follow his every move.

The story is told like a slow-burning romance story, so there's a lot of text and options to explore

[From link]