From the cover I thought he woud have resurrectd and joined hands with other people he knew were strong and would have kept silent on him, instead he goes to a dungeon, shoots a "raise the dead" and bam, all the harem is there, is clear from their reactions that they have someone able to predict the future, were forced to hide in the dungeon a century before and died there, the dungeon being turned off and hidden just strenghtens this theory.
But the rumors the MC heard about are weird, a dungeon no one visited in a century with a camouflaged gate and he just happened to know about and find it after a short search, the girl with the foresight must be incredibly powerful...but then how did the demon lord group got forced in such a situation? Maybe the future she sees is random but 100% to happen.
Is even possible that the Maou lady programmed the dungeon to go inert in a century or when a solo healer entered it.
The first chapter was decent but unless explained the second one is Deus Ex Machina overclocked.