Five years have passed since mysterious dungeons emerged worldwide, unleashing monsters into our realm. Ordinary individuals have embraced the mantle of adventurers, engaging in combat with these fantastical beings and delving into dungeons. Among them is Karaboshi Haruki, a 27-year-old novice often disregarded by his peers for his lackluster monster-defeating and treasure-acquiring track record. Feeling outmatched by more seasoned adventurers, Haruki stumbles upon a unique opportunity when a dungeon materializes beneath his own home. Could this be his chance to hone his skills? To his delight, he uncovers a Skill Board that accelerates his leveling process, propelling him into the dungeon-crawling escapades he has always envisioned.