Kazoku o Shokusu to Iu koto by Eroge Honpo - Adult Sex Game

Yuki lives with his mother, who is very strict to him. One day, Junko, his aunt, and Sayori, her daughter, start living at his house. Days later, Sayori accidentally sees Yuki masturbating. Yuki thinks she will dislike him, but Sayori smiles and says, "You don't need to hide it...."