Yashahime: Princess Half-Demon: Season 2, Episode 6

2 - 6: 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!