@Peridot the... inverse heroes I'll call them, seem to have a different world that seems to be just as in danger as this one and this one's destruction by the waves will somehow save theirs. I lean towards colliding parallel worlds, the friction creates the waves and one of them is gonna have to be displaced in the end.
Also, why does Glass look like she got like fifteen years younger? I swear she looked borderline old enough to be Naofumi's mom before and now she looks barely out of middle school. I mean, manga ages are hard to pin down, but still.