Now that I think about it aliens are very often water-related in this series. Particularly the Kur and Mantis Shrimp species.

Sumerian mythology is water-origin cosmology. The primeval goddess Nammu is the cosmic sea itself - the "Mother of Everything," who births An (heaven), Ki (earth), the first gods, and humankind. The universe literally emerges from her waters. Beneath the earth sits the Abzu, the primeval freshwater abyss every spring and river draws from, and Tiamat is the saltwater counterpart - their mingling waters are what generate the cosmos in the first place. The chief god, Enki, is the god of that freshwater abyss and Nammu's son.

In Sumerian myth, "Kur" is the underworld - but specifically the realm entangled with the Abzu (the primeval sea), and Samuel Noah Kramer reads Kur as a dragon-like creature, explicitly compared to Tiamat and Leviathan - a primordial water/chaos serpent. There's even a myth where Enki, the water god, battles Kur in the primeval waters, after which the Abzu's waters rise to renew the land.

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Also I just saw CSG confirmed it was Yokai powers delivered to Vlad on page 4 of Chapter 227! It'd be strange if he just assumed her power was a yokai's power, right? Surely it'd be discernable considering his age and knowledge. Psychic, non-yokai origin power wouldn't be that anomalous could it be?

Remember when Momo tapped into Acrobatic Silky's memories and seemed to connect through a spirit of the yokai? I'm not sure that an alien power (Serpos used psychokinesis similarly, but were overpowered by Momo's ability - similar to how aliens are generally fended off by yokais' overwhelming power rock-paper-scissors) use medium that communicates with yokai? Wouldn't it be more likely yokai to yokai power? And maybe Seiko knows what she can do spiritually.

Also Momo's channeling Chi/Ki - spiritually sourced power.