Eromanga Sensei

Eromanga Sensei is a light novel series that received an anime adaptation in 2017.

The story follows Masamune Izumi, a first-year high school student who also happens to be a light novel writer. Living with his younger stepsister Sagiri who's a shut-in, Masamune gets his novels illustrated by an anonymous artist named 'Eromanga Sensei', but one day he gets the shock of his life when he finds out that his partner was Sagiri all along.

Episode 9
Masamune is invited to a writing camp taking place on a island owned by Elf's family.

Episode 10
Masamune's yukata gets slightly loosened.

Episode 12
The girls try to strip Masamune, and later he walks out after taking a bath.

OVA 1
Ely posts pictures of Masamune at her family's island on social media.

OVA 2
Masamune asks Sagiri to wipe his back while he's changing his shirt.