Daisuke Kobayashi is a young man who, as a boy, was taken by government scientists and transformed into an assassin as part of a project to create magical super-soldiers to compete with other nations in the world.
After a countless number of killings, he eventually went insane and sought to empower himself in order to exact revenge against his oppressors. In the end, he was killed due to a magical overload.
Reborn as Leonis, the third son of the powerful Camellia family, he finds himself in a world far different from his own: a Victorian-esque world where magic fills the air, steam train engines roar through the streets, and streetlights illuminate the night sky.
Leo is faced with many challenges ahead of him—dealing with his newfound emotions, being pitted in political drama, attending a magic academy where he sits at the bottom of the food chain, encountering various powerful entities of different shapes and sizes, and so much more.