Kazoku ~Haha to Shimai no Kyousei

The older sister: Nagisa. The younger sister: Fuuka. Mother: Otoha. The main character's father's remarriage creates a family of three people who are not related by blood. Although the relationship is amiable, the new family members are beautiful women, and the protagonist is troubled by the closeness of his family. He sees his new relatives as women, and his lust grows everyday.