They're beast people and the uke is a human. It's a polyrelationship. The seme are bear and a lion, if i remember it correctly. I forgot about the main plot of the story. Idk if it's updated now.
im going to make a suggestion as a joke, and while im laughing my ass off, i will also be feeling pain from how unfunny it is to suggest this in response to your plea, hold up
i love bls like this not those with child looking uke