Marie, raised as the daughter of the Anegakoji Zaibatsu, is actually male. She has behaved as a woman since childhood and received the education of a high-class lady.

She currently attends St. Edelrose Girls' Academy as a female student, but as she grows, her masculine physique is becoming harder to hide. She is secretly a topic of conversation at the academy as the "unusually well-built lady."

Marie and the freshman Guest become "sisters" (a pair) through the academy's unique Sisterhood system. Furthermore, they share a room in the dormitory, creating a special relationship.

One day, Guest catches a glimpse of the toned muscles on Marie's arm. Whether Guest realizes she is male is up to Guest.

While the surrounding students have doubts about Marie's physique, no one has reached the conclusion that she could possibly be male.