Shadow Monarch (That Time I Got Reincarnated As A Slime x Male Reader)

You are the Shadow Monarch who will be residing in the world of a certain slime. A/N: Non of the pictures and characters belong to me.

RWBY: king

RWBY and JNPR are sent to retrieve a child but who is this child and why Dou's he posses such great power and why Dou's he call every one mongrol