Yagami Tsubasa is a high school girl living alone. After her parents passed away, she used to live with her older sister, Sawa, but when Sawa was assigned as a teacher at a boys' boarding school, Kousei Private Academy, they became separated.

Even though being apart, they were still in contact with each other, however...... One day, Tsubasa suddenly loses contact with Sawa. Despite filling for a missing person, or making various inquiries at the school, the search does not progress.

Together with her best friend Mizumori Sei, they start to look for Sawa themselves, and eventually end up finding out numerous unpleasant rumors about the school. The groundless rumors on the Internet...... After reading these unpleasant contents, Tsubasa is afraid that Sawa's disappearance will be buried in the dark, so she becomes desperate. She thinks about moving into the school and start looking on her own, but even so, there is still a big problem. Because, Kousei Academy is a "boys' school," while Tsubasa is a "girl." So Tsubasa comes up with the idea of "dressing up and moving in as a boy." It appears to be reckless, but with Sei's help, she is able to infiltrate the school as a boy under the name Yagawa Tsubasa.

As she continues her search, she meets an art teacher who is Sawa's best friend, Urabe Kanna, and a girl who happens to be at the school for some reason, Yui Noeka, little by little​, she gets closer to the truth.

Sawa is almost within her reach......but at that moment, Tsubasa's identity is revealed to a certain opponent. A man who is deeply involved with the dark side of the school, now completely under his thumb, Tsubasa has to do what he orders......

And so, will Tsubasa be able to reunite with Sawa? Or perhaps, will both her body and soul be corrupted in this Garden of Men......