Hasumi Ryuuji, dubbed as the "strongest soldier of the modern era," is transported to the depths of a dungeon in a parallel world during a mission. As he explores this unknown territory, he witnesses adventurers being assaulted by monsters, but a celestial voice guides him through it all. With his exceptional combat tactics and physical prowess, he effortlessly conquers the beasts, becoming a hero in a world where monsters surpass the power of adventurers. After rescuing the adventurers, the group faces off against a dragon - Hasumi's quick-thinking and tactical genius coupled with his advanced weaponry leads them to victory. Although questioned about his identity, he simply claims to be a soldier. Thus the story commences, with Hasumi abandoning his past as a special forces soldier to embark on new adventures in a different world.
