You threw the very answer for your question bud. Bakarina was the first, it got popular, now people are flocking to make something of the kind.
Still, i have to say that Isekai as a whole has a bunch of decent titles out there, but they're flooded by the Morton's fork rule of exponentially higher numbers of trash titles. Argate Online is a fun Isekai that's full blown into OLD SCHOOL artstyle for the manga; Galactic Navy officer becomes adventurer makes Isekai through Sci-fi exploration of universe; Manuke FPS runs the typical Gate esque "what happens when you bring something ENTIRELLY alien to a medieval fantasy universe (modern guns and AFVs and sci-fi power suits).... and these Villainess being reincarnated person are popular because they spin things anew (in this subgenre, not so much, but there's plenty other methods to spin the wheel), should check the one where MC is reincarnated as the BUTLER of said Villainess....
In short : the faces are humans. The shadows are fairies that specializes in mimicry. Those fairies are actually very weak, they become powerful each time they made physicals contact with their faces. And their final evolution is to take over the human body entirely... which resulting the death of the face I assume.
That is pretty sad. Reading it more in depth and understanding way more, and then reading the manga and seeing what you read, but also understanding the emotions of the characters. That's twice the damage ;-;