Koinaka -Koinaka de Hatsukoi x Nakadashi Sexual Life by eRONDO (Jap)

Set in a rural town, Kouta is the only son and heir to the Mikomori shrine in the small redeveloping town of Tsumagoi-chou which had been declining in popularity. He didn't have any interest in inheriting the shrine. Instead, he focused on his studies, aiming to be a civil servant upon graduation. His widowed father talked about marrying a young girl, but then he suddenly disappeared. That girl Erina came to live with him, along with her younger sister Motoka. With the help of his childhood friend Mio and a few supporters of the shrine, they managed to continue living normal lives. One day, Erina brought home a girl Mai, who called herself his fiancée. One thing led to another, culminating with Erina ordering him to get her pregnant.