I'm Giving the Disgraced Noble Lady I Rescued a Crash Course in Naughtiness season 1 episode 9
Episode title: Naughty Visit to the Parents
Hearing that Charlotte's little sister is in trouble, Allen and the others rush over to Allen's hometown. They're welcomed by Allen's uncle, Harvey, and his aunt, Liselotte. As they figure out Natalia's situation, they're forced to pretend being lovers.
