Hitozuma♪ Kasumi-san 2 ~Oku-sama - Miboujin Owner to Kyoudou Seikatsu~

Main character gets separated from his niece after their intimate relations uncover. One day younger sister of the niece introduces him to a part-time job in a pension at a summer resort. Protagonist jumps at the opportunity welcomed by the hospitable resort owner and inhabitants.

[From vndbreview]