Mirea is kinda right tbh. The elf is one thing, but Naga is definitely beating them up and capturing them once she gets her mana back and has a way home. I wouldn't put it past her to kill them (I mean, that wouldn't actually happen because this isn't that dark a story, but Mirea and Naga don't...
Way more interesting setup than 90% of isekai. This is a cool mystery to start the plot with, and I'm glad it isn't actually a videogame style world (that tropes ruins the fantasy for me).