The young knight Tio, who had been on a journey to save the world with the female hero, was expelled from the party due to his lack of strength. On the night of his expulsion, Tio has a dream. It is a dream of a magic emperor from hundreds of years ago, who used black magic to overwhelm the demon that had brought humanity to the brink of destruction. Tio remembers that this magic emperor was his past life. He also recalls that in the modern world, the black mage, which is considered a bottom-tier class, can become the strongest class if mastered using a certain method. With his memories restored, Tio changes his class from knight to black mage and becomes known as 'the strongest'—. *Also published on Kakuyomu.