Rascal Does Not Dream of His Student (light novel) — Hajime Kamoshida

MINISKIRT SANTA'S COMING TO TOWN!Mai is in danger, and the only clue Sakuta has is a cryptic message from himself saying he needs to find Touko Kirishima. The problem is that even though he knows how to contact her, Touko seems completely uninterested in helping him. There must be another way. The answer might lie with his new student, Sara Himeji, a first-year at Minegahara who may have gotten her own little supernatural present. He'll have to figure out something quick, because Touko is planning to release a new song and there's no telling what fresh chaos that might bring…