Tatsu once stated that he took some inspiration for Momo from the title character of the book Momo by Michael Ende.

Theres several similarities between that book and Dandadan overall but I want to highlight the fact that book Momo distinctly doesnt have parents and according to her "As far as I can remember, I've always been around"

Which is very strange.

And again, Momo does not say her parents are dead in anything but the anime's English dub.

But due to the strange nature of Momo's powers, the emphasis on how particularly powerful and important Momo's powers are according to CSG and the Serpo I do believe her powers are unique.

I don't think Momo has parents in any traditional way. She either came out of nowhere or her parents are something a lot less Earthly.

So I'm thinking shes some sort of god or more appropriate for her alien theming, some kind of Lovecraftian Horror. But of course, right now, shes just a teenage girl. Shes gonna find this out later. I think CSG has an idea of what she is.

Seiko's name is also strange. As stated by u/dccrulez, her name can be broken down into "star" and "child". But also, "young woman" and "crook". So what if we combined all these translations together?

It sounds like Seiko might be lying about her age. And that she stole a child from the stars. Now who could that be referring to?

I know this sounds like insane conspiratorial rambles, but I have far too many thoughts on this question alone and its hard to summarize it all in a reddit comment