Kedamono Arashi -Love Me Baby!- summary:

In this world exist "normal" human beings and those with ears called "beasts". Beasts have a unique body that experiences heats/ruts and pregnancy between the same s** is possible. Akira, a veterinary specialist, meets Sougo, a beast who has lived an arrogant life based on his instincts, and after many twists and turns, they become a couple. Akira and Sougo are blessed with three cute sons and are living a happy life, but one night, a sad-looking Kazuhisa visits the Kijima family.+