In a time and place where one's soul can be morphed into a weapon, there are modern-day magicians called Mage Knights. Although Kurogane Ikki is a student at an institution that trains Mage Knights, he has no particular talent in magic and is labelled the Failure Knight or the Worst One. Getting way less than average marks, he is forced to repeat a year. But with the arrival of a new head of the institution, a new rule is created: knights whose abilities are compatible, as decided by the board, must share rooms and train together throughout their school years to maximize their abilities.

Ikki's room-mate turns out to be Stella Vermillion — a princess from a foreign country and a rank A knight: the type of genius in magic that only appears once a decade. When Ikki walks into the room while she is changing her clothes, it causes a huge misunderstanding that eventually leads to a duel between the two. The punishment for the losing side is the Eternal Submission to the winner.

Forced to live the same room and practice magic together in the upcoming school years, how will Stella and Ikki's relationship evolve?

Source: Baka-Tsuki

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