Hidan no Aria: Butei ga Kitarite Onsen Kenshuu

Tsuzuri takes Kinji, Aria, Shirayuki, Riko, Jeanne, Reki, and Muto to a remote bathhouse for special Butei training. A mysterious fog, a strangely youthful elderly owner, and a ghostlike boy quickly turn the retreat into something far more unsettling than a simple visit to the hot springs.

Memories begin slipping, time seems to repeat, and members of the group vanish from where they should be. Kinji and Aria must uncover the truth behind the bathhouse before its illusion traps them in the same strange night indefinitely.