There's nothing but youkai who can live hundreds of years underground

They slowly start going out

Then they can make children and have a wedding

That's how it normally goes

As for the surface it's based on humans

And their relations go awfully quick

They can start dating, marry and have children in the same year

...That's only the case for humans

No Youkais from the surface are also based on humans

So, Satori-sama

Haven't you been slacking off

It's not good if you ask me