I've been wondering why the fuck people are so shocked about the reincarnation aspect of the story, but it looks like someone's changed the description since I started reading this series; it used to mention that the MC was a powerful demon reincarnated as a human who seeks out his former comrades to rebuild their dungeon.
I was more surprised that the prologue lasted so long when most reincarnation stories dedicate maybe a quarter of the first chapter, if that, to the MC's previous life.