Yes this is a little bit of a stretch but I liked this idea so let's roll with it. Basically I had asked a friend of mine what he thought of my last idea of Sienna having a kid with Ghira, but he misunderstood me and thought I meant that Blake was Sienna's kid and I wound up liking the idea. So here's the idea, Sienna and Ghira had a kid and that kid was Blake. I know you may ask, but when two different faunus have a kid, that kid has some random animal trait. Well I have two counters to that.

1. We have different breeds of cats have kittens that are basically a mix. We even have tigers and lions having kids together, so its not crazy to say that a Ghira and Sienna could have a kid that just takes more after her father.

2. Every example of two different faunus having kids is two really different animals, like a wolf faunus and a bull faunus. But Sienna and Ghira's animals are way closer than a wolf and a bull, so it could easily be said that the little random thing doesn't happen.

Okay, there's another "theory". Not so much a theory but more of a fun little idea, but still, its an idea.