Bokura ga Koroshita, Saiai no Kimi

Six friends attend the elementary school reunion, each intrigued by the invitation they received. Their host, Kaoru, appears a bit eccentric, but they don't really react much since none of them remembers him. On Kaoru's suggestion they agree to play the murder mystery game... that is, until they realise their roles are themselves, with their secrets exposed, locked with no way out, and their host is dead.