Haitoku no Kakure Boseiai ~Yasashi Sugiru Ecchi na Onee-san wa Okaa-san!?~

Having been separated from his mother when he was a child, he never learned about her whereabouts. But after doing some research, Takuma manages to finally find a town where she might live and decides to settle down on here.

After moving to the town, he meets an older woman, Fuyumi, who lives nearby.
Takuma begins to feel at ease with her, and she takes care of him in his daily life.
In time, Takuma falls in love with her and eventually they cross a line.

However, he later learns the truth.

[Translated from the official website]