To Save the World, Can You Wake Up the Morning After with a Demi-Human?, Vol. 1 — Rekomaru Otoi

Long ago, the Chosen One defeated the Demon King and brought peace to the world…not that it matters to ordinary high school student Hironori Tabata. But word is the Demon King's coming back, and the only thing that can stop him is what's in Hironori's pants. Before long, demi-human girls are throwing themselves at him, hoping to give birth to the next Chosen One, and Hironori has to worry more about saving his chastity for the girl he loves than saving the world!