Yashahime: Princess Half-Demon S01 E30 Hisui the Demon Slayer

Setsuna is kidnapped by Princess Aiya, daughter of the deputy shogun. Wanting to escape her studies, Princess Aiya begs Setsuna to be her body double for a day, but the princess’s new tutor turns out to be Hisui posing as his older sister Kin’u!