Mui and Tsuganashi of the Ruined World - S1.E4

Takeshi and Ida are at an early-morning practice session trying to master control of their magic. When Kurumi finally arrives, it is with the news that Mui did not return to the girls' dorm the previous night. From the looks of a map they discover on her desk, it seems Mui has again gone off to try to get back her older brother Tsuganashi.