Huh. Interesting. Normally, when we get these isekai returnee series, the MC was 100% unaware of the supernatural being a thing pre-isekai (if it even was a thing and not some god's fuckery); here, though, it's established that the supernatural is a thing and that the MC was intimately familiar with it before getting isekai'd.
Neat little twist (emphasis on "little") to an otherwise standard setup.