Ichinose Yuto was a modern-day Holy Knight, born as a descendant of the Crusaders of medieval Europe, who became the youngest ever to hold that title. During a battle with assassins, he sacrificed himself to protect his comrades. When he awoke, he found himself reincarnated in another world as Luca, the son of a noble family. His new life is one of training in swordsmanship and magic alongside El, a slave girl of the same age who works as a servant in the household. Together, they aim to enter the Galleric Academy, the world's only school of its kind, and Luca's ultimate goal is to become the strongest magic swordsman in the world.

The story follows Luca as he passes the academy's entrance exam and soon joins his new classmates in a dungeon expedition. There, they encounter an unexpected enemy that forces them into battle. As Luca navigates his second life, he applies the combat experience and sword skills from his previous existence while learning to wield magic in this new world. The narrative centers on his journey alongside friends and allies, engaging in fierce battles against demons and other threats in a fantasy setting where swordsmanship and sorcery combine.