.....Okay so what kind of Yokai could do this? Because Momo and Ken weren't poofed out of existence but Seiko lost over 60 decades of age in one go X'D

Awkward considering I believe Seiko enjoys drinking and smokes... My guess is Turbo Granny and Acrobatic Silky teamed up and ended up spawning a gestalt entity or one already existed that thrives off of embarrassment and nurturing, possibly de-aging by devouring characters like Acrobatic Silky with a comical, transparent ball-pit stomach? IMHO IF Turbo Granny shows up a rat might be a good choice, though her later Maneki(?) Neko form would be counter to that. Acrobatic Silky could be a weasel? Anyway, know my randumb inputs are just that, but I've got insomnia and am aching so TTFN.