Kill each other...for science! The class of '89 is trapped in an elite school killing game. Investigate, solve, and expose your classmates in Kumitantei: Old-School Slaughter, an episodic murder-mystery ADV card-battler inspired by retro anime.

Himari Sanada is an ordinary girl who's had the greatest Imperial honor for students thrust upon her: an Absolute title and admission to the prestigious military research academy Janus Institute. The morning of her first day however, she does not wake up in her bedroom, instead finding herself trapped alongside 15 other Absolute students within a decaying old bunker seemingly built by their new school. Confronted by a strange two-faced cat, the class learns they've been brought here as test subjects in a kill-or-be-killed Apathy Experiment designed to fracture and drain their very humanity.

Himari, the Absolute Barista, desires to overcome the eccentricities of her fellow participants and make friends, but is often instead forced to investigate and solve their grisly murders. Bond with the others to learn their Skills, scour diverse crime scenes for Evidence, and then leverage it all in the stylish and frantic Clinical Trial.

Will they band together to uncover secrets of the past, or lose their humanity and lives in the present?