Akimitsu Tsukasa, who was summoned to another world along with his classmates, ends up wandering alone in an unfamiliar world after the betrayal of his friend, whom he considered his best friend. Tsukasa, who arrived in the city of Aigiyu, inhabited by the "demonic" race, relies solely on his "gift" received upon being summoned: an outdated magic called "runes." Thus, he lives as a "freelance mercenary," leading a life on the edge of death every day. One day, he is suddenly visited by her childhood friend, Matsuzaka Mihono, who asks she to help her sister, Shihono. What will the agreement between Tsukasa and Mihono be?