At first I thought this was a narou series, but no it's an original series. Fascinating.
The premise is okay so far, I guess. A lot of the exposition felt forced, and it feels like you could've cut some of that out. Like, if Hiyo remembers some of her past life, why have the maid blurt out the rest?
Also, with that credit page... you got me. Now I want an Avengers-like movie where six old men who were reincarnated as little girls come together to save the world from an evil threat who turns out to be their natural opposite: a little girl who was reincarnated into an old man. That one's free, Netflix.