This is an omegaverse where manbeasts and humans co-exist.

Manbeasts can only be born from an omega (Ω) human. Kai is a young Ω abandoned by his parents. He was picked up by Roald (α), the head of the Siegfried family, the most powerful manbeast clan in the country, to bear their children.

Up until then, he was treated as a nuisance by those around him, so he was drawn to Roald who treated him as a human being. Before he knew it, now he dreams of becoming a pair with Roald...

However, he learns that the Siegried family doesn't form pairs and goes through multiple omegas to leave more descendants...And the destiny of an omega in heat is to go with multiple manbeast partners as well...