STARLESS: 21st Century nymphomaniacs.

Story

Based on the erotic game by Empress. Sawatari Yukito was looking for a summer part time job, when by chance he came across an advertisement in a job search magazine for a position with really nice wages. Upon quickly contacting the employer and learning that the position had yet to be filled, he applied without delay. The job was as a live-in servant at a mansion. His first day of work arrived. Upon arrival at the mansion deep in the mountains he was surprised by the size of the grounds and the palatial building itself… appropriate for the richest of the rich.

Synopsis via AniList (English).