Mariya Shidou is the deuteragonist of the story. He is a cross-dressing boy who attends Ame no Kisaki as a girl as a means to win the chairmanship of both the all-male and all-female schools where his late grandmother served as the ex-chairman for both.
He deeply respects and loves his grandmother and does not care about actually winning chairmanship. He simply wishes to honor his grandmother's request. He appears to genuinely care about others though this facade is often hidden through some excuse he has crafted for himself.
When Kanako first meets Mariya, she is instantly attracted to his playful femininity and kind attitude. He often teases Kanako by playing with his long blonde hair, speaking in a soft voice, and smiling sweetly. However, Mariya turns out to be quite sadistic in nature and generally adjusts his personality to reflect whatever situation he is in. Mariya's beauty and feminine gestures are so convincing that the entire school, including the faculty, have no idea of his true sex.
Mariya is quite short, reaching at most up to the height at the tip of Kanako's nose, and shorter than Matsurika. Because of the switching with his sister his original name was Shizu instead. His birthday is on March 3rd and he's a Pisces. His height is precisely 160.3 cm and his blood type is A.
At first glance, a seemingly kind, and selfless student, Mariya's true personality couldn't be further from that. A cunning, and incredibly sadistic boy who enjoys nothing more than torturing Kanako, or his twin sister Shizu, although he claims the treatment of the latter is because of his love for her.
Mariya attends the prestigious Ame no Kisaki Catholic girl's school, due to a rather silly bet thought up by the previous head of the school, who in actual fact is Mariya's grandmother who he deeply cares for, and holds in high esteem. Mariya keeps a rosary she once owned as a memento. The bet in question is that Mariya, and his twin sister each attend schools for the opposite gender, and if they can stick that out for three years, the winner shall become head of both schools. There is a catch, and that must be that nobody can find out their true gender. When Shizu comments that Kanako knew his gender, Mariya finds a loophole.
He is usually accompanied by his blunt and passive maid Matsurika, who helps him with putting his image together, including tying up his corset.