Ace Cross is not your typical NEET, although he has all the making of one and is recluse, he is still a very outdoor type of person. One day he is killed (by a truck no less even after dodging off the road) his soul was going to white light in the sky (the sun) but before he could arrive a magical circle appears and he is pulled in and given a second chance at life in a magical world under the most cliche trope of anime, as a summoned hero.

He isn't 'the' hero though, he got the most uncommon hero class and something that has been extinct in all the nations blocking the advance of the demon lord. That is the Dungeon Maker. As a very unusual class that makes not only death traps but proper dungeons with ecosystems, this is the life of humanities first dungeon maker in 1,000 years since the demon lord war began. This is not just a story of battling the demon lord but also of how our heroes making a new life force themselves as all of them died in their original worlds.