Raised by the legendary mercenary Ains Worker, the girl Sierra was sent to the royal school in the capital to learn how to live an ordinary life. Having spent her whole life on the battlefield, she has to rely on a notebook from Ains for tips on how to act like a normal person. But no matter how hard Sierra tries to act unobtrusively in school, her skills become obvious to all.

When she meets the girl Aruna, they become friends, and Aruna helps Sierra stay out of trouble. Their relationship deepens, not knowing Aruna is caught in a plot for the inheritance of the throne…