Its a collection of stories with the same sort of theme. There are these beings...usually gods i think who are able to take human form either when they fall in love or when their love is returned....I think that's how it works. It's not an Omegaverse but somehow some of the men in the stories have kids/talk about making kids together.

One story is about a dragon god and his boy sacrifice
Another is about a beautifully singing bird who brings spring with his song
And I think there's even one about a horse being ... and a ghost boy is in this one as well i think.

Mauri to Ryuu by Moto Haruko