Synopsis
Mitsuru Sasayama serves as an Enforcer in Division 01, a short-tempered, sharp-tongued man whom Shinya Kogami nonetheless finds genuinely amusing and comes to respect deeply. He turned himself in to police as a teenager after fighting back against his abusive father and believing he had killed him; the father survived, but Sasayama's path into rehabilitation led him, ultimately, into the Enforcer corps.
Assigned to Division 01 under Kogami and Nobuchika Ginoza, Sasayama becomes the investigator who finally uncovers the lead connecting a string of gruesome killings — later called the Specimen Case — to Shogo Makishima. That diligence gets him captured, tortured, and killed: his body is dismembered and preserved through plastination, put on display as one more of Makishima's grotesque trophies.
Sasayama's murder becomes the turning point of the entire series, driving Kogami's crime coefficient into latent-criminal territory and setting him on the path toward revenge that defines the rest of his story.
