Tokkyuu Tansakushi he no Kakusei

Dungeons have suddenly appeared all over modern-day Japan, and the people who challenged these strange, other-dimensional areas despite knowing the danger are dubbed "explorers". Tenji Amashiro, a high schooler aiming to become a professional explorer in order to look for his parents who went missing in a dungeon, built up his skills each day through a part time job carrying baggage for an explorer's guild. But one day, Tenji gains a strange and unusual power after experiencing "hell" in the vast, innermost part of a dungeon... And so begins his path from being a weak, powerless young man to becoming the ultimate, unparalleled explorer! Source: MAG Garden