Rika Mizushima is the older sister of Ryo Mizushima and a Yokohama Minato High School graduate. She shouldered significant responsibilities in their childhood, caring for Ryo while their parents were occupied with work commitments. This established a dynamic where she maintains a watchful, supportive, yet firm presence in his life as he navigates high school and competitive badminton.

Her personality blends brilliance and eccentricity. Recognized as Yokohama Minato's "madonna" during her time there, she possessed notable charisma and popularity. She harbors a distinct ambition to become a "great person who creates history," a drive shaping her outlook and actions. Her interests include an admiration for Leonardo da Vinci.

She has waist-length brown hair, green eyes, and stands 160cm tall. Her birthday is January 30, placing her under the Aquarius zodiac sign, with blood type A.