Actually, there is, but it's dripfed throughout the chapters so if you're not paying attention it's easy to miss, but they seem to be creatures tied to obsessions/fetishes with body parts, either the remains of people who fell into the gap on their own or as some sort of manifestation, we're not entirely sure, but we know there is a link because of Hebizono and her ne-no-kami serpent that is also a part of her- or perhaps IS her, but with her consciousness returned in some way, so she can also take on human form; the specifics aren't sure but that she and the serpent are intrinsically linked is a for-sure.
This chapter's flashbacks also are giving us some information about how people end up slipping into the gap, because something in their lives is leaving them so unsatisfied that they just slip through a crack. Neshos just make it much easier because they're already entangled with that slip-dimension.
She had a short moment where her back was shown and an onmyodo talisman is seen there like the one that was attracting them in the last encounter with him they had; she was being controlled by the onmyoji. But also remember they eat even the existence of the thing they consume; that was what the loss of the hair was showing us- they totally forgot that it was even a thing they had to begin with, and that numbing of memories also seems to remove the fact that they're being preyed upon from their memories, too.
Except that I don't see how that explains why, if they
are people who were consumed before and twisted, they continue doing it to others, and what the end goal of Glasses Man is with all of this or how the Snake Girl actually factors in.
We have some of the mechanics of things, certainly. We know
how some stuff works, to a degree, but unless I missed something on a re-read, the
why of it all is still one big question mark.
Why does the gap exist? Why is it attached to sexuality? Why are people disappearing from reality, and why is the MC the only one who remembers? What are the goals of Glasses, and why do young girls factor into those plans (first MC's younger sister and now Fuu-chan)? What is Snake Girl doing that she's some sort of rogue semi-antagonisr, if she helps and hinders Team MC in turn?
We have nothing on any of that. We have a vague goal of MC's, we have an antagonist with zero explanation or clearly-stated intention, we have sex as a means of worldbuilding and pseudo-combat, and every chapter leaves more questions than answers.
You yourself said we don't have the "why / specifics", after all. And that's kind of important, if the author wants readers to stay engaged. Endlessly piling on mysteries with no payoff and more and more tragedy every arc does not make for a satisfying read, and the ecchi factor, in my mind, doesn't buffer those issues.
