OVA: Magical Girl in Hot Springs Inn

Illya and co. go to a hot springs inn, where Rin and Luvia are carrying out a secret mission. During the trip, Kuro discovers that the hot springs cause a greater drain on her mana than usual, so Illya and Miyu make up for it by doing other fun activities with her. Later that night, the girls investigate a magic point, which creates a hidden hot spring and rectifies the properties of the hot springs in the region.