Itsuki Myoudouin is the student council president at the Myoudou Academy Junior High School. She is the granddaughter of Gentarou Myoudouin, the president of Myoudou Academy. Because she looks and dresses like a male, she is often mistaken as one by new students, and even people who know about her situation state that sometimes they forget that she is a girl. She crossdresses because she chose to take the place of her older brother, Satsuki, who is too sick to act as the heir of the family dojo. Her Heart Flower is the peony, symbolizing her rebirth as a person and her noble background. Itsuki's Cure ego is Cure Sunshine.

Befitting of her image and upbringing, Itsuki is a wise and princely young woman who is very formal with others. She is calm-tempered and kind, willing to help friends and strangers alike, but she can also be stern when it's necessary and has no problem stepping in to defend those weaker than her. She is brave and compassionate, but this will not stop her from unleashing rage on those who hurt the innocent. She is strongly admired by others for her strength in character and as a person, which played a part in her struggle to find a compromise between who she thought she had to be and who she wanted to be. Itsuki has a fondness for anything cute and girly. While she is normally gentle and seems to be on the introverted side initially, she becomes excited by things like toys and clothing. When she realizes she can embrace this part of herself, she begins to show it more openly to others.