@sketches
it hasn't gone into much detail so far, but based on what we have seen I believe the following 2 points on magic to be true:
1 - otherworlders who came from lands with magic can still use their original world's magic here and can probably learn this world's magic on top of that
2 - MC came from a version of Japan from a magicless earth-parallel and has only learned this world's magic, but is able to cast it without saying a spell incantation which is a rare talent in and of itself (but intrinsically different from true otherworldly magic) but the fact it is so rare a talent misleads many of the locals into thinking she actually possesses otherworld magics
*3 - not related to magic directly, but otherworlders seem to be at least semi-common in this world, and, as per the usual trope, possess rare and/or unique abilities that range from difficult to outright impossible for normal people to acquire, which leads to otherworlders being sought after by everyone with any degree of ambition and/or ill intent...and if meeting with the wrong people first, likely ending up enslaved or worse for the sake of harnessing those talents