Hasumi Ryuuji, the man called "the modern era's strongest soldier", someone who can make numerous difficult strategies a success, was transferred during a mission into the depths of another world's dungeon. A "heavenly voice" echoed inside his brain guiding him — "Welcome, the hero from another world" — as he encounters a scene in which adventurers are being attacked by monsters. However, making good use of his superior physical abilities, discernment, and hand-to-hand combat abilities, he succeeds in easily making quick work of the monsters.

In this other world, where adventurers are existences weaker than monsters, Hasumi, who can suppress his target even with just a knife, was someone regarded as a hero due to his outstanding abilities. Hasumi decides to cooperate with the adventurers he rescued, but they are attacked by a dragon, falling into a critical situation. Nevertheless, he leads his flustered comrades, coordinate them and makes an attack opportunity to appear.

Moreover, after he summons modern firearms with a "weapon summoning" item, he kills the dragon in one shot by accurately targeting its weak spot. In front of this man's tempered body and intellect, someone who is asked "Who the heck are you?" answers "I'm just a soldier", even the mythical-grade dungeon is not a threat?!