Villain: Perpetrator Chase Investigation S1E1

Saeki Shuichi was a detective, but he quit his job. He now works at a detective agency. One day, a couple asks the detective agency to find a man named Sakagami. The man killed the couple's son and served at a youth detention center. Kogure Masato is the director of the detective agency. He tells Shuichi to work on the case. Shuichi is also part of a victim's family. When he was a child, his older sister was murdered. While Shuichi watches Sakagami, the couple asks him to find some materials which will allow them to forgive Sakagami or not.