Rascal Does Not Dream of His Student

Book 11 of the Seishun Buta Yarou series.

A miniskirt-wearing Santa appears before Sakuta, calling herself Touko Kirishima and cheerfully informing him that she’s been handing out presents—Adolescence Syndrome. Apparently, one of the lucky winners is Sakuta’s classmate from middle school, Ikumi Akagi. According to urban legend, posts tagged #dreaming are filled with prophetic visions, and Ikumi is using those posts to play hero. Sakuta sees the results of this first hand when he spots her saving someone. And then a poltergeist suddenly attacks, and this is somehow his fault?! Solving all this might require delving into Sakuta’s unpleasant past...

(Source: Yen Press)

Book 13 of the Seishun Buta Yarou series.
IS THE REAL MINISKIRT SANTA IN A SEA OF FAKES?

Sakuta thought he’d already accomplished step one: Find Touko Kirishima. The next step was convincing her to help protect Mai, but that proved easier said than done. In the process, however, he makes a confusing discovery: There are multiple Touko Kirishimas! The Touko he knows may not actually be the person he’s looking for! With clues from his friends’ prophetic dreams, he gets closer to figuring out exactly what danger awaits Mai, but he’ll have to sort through the fake Kirishimas and determine who’s the real deal before it’s too late… 
(Source: Yen Press)