Bakumatsu Rock: Mystery! Onsen Kaijiken ze yo!!
Japanese title: 幕末Rock 湯煙推理劇[ミステリー]! 温泉怪事件ぜよ!!
Type: OVA
Episodes: 1
Source: Game
Genres: Mystery
Studios: Studio Deen
Duration: 23 min
Rating: PG-13 - Teens 13 or older

An incident has led to someone's death at Teradaya, which the gang went to for a day trip. A "69" on the victim's leg will be the key to solving the mystery.

(Source: MAL News)