According to the god Origin's prophecy, the girl Flum was chosen to be one of the members of the party that were foretold to defeat the Demon Lord. Everyone already had achievements to their name, as well as the strength to back them up. However, only Flum did not possess any combat prowess, and all of her stats were 0 due to her rare affinity. While being constantly berated, she continued to put great efforts to be useful to the heroes.

Until one day, she was tricked by one of the party members who said that she "was not necessary anymore" and sold off to a slave trader. Flum was forced to live as a slave, locked away and barely fed. There she encountered a "cursed sword" and realized the true power of her rare affinity, "Reversal." The girl, who acquired the power to fight, was indifferent to the Demon Lord and decided to live peacefully as an adventurer alongside a slave girl she met.