Umeda Rio is Hokuto's younger sister and is about the same age as Mizuki. She goes to Osaka High's sister school, Saint Blossom. She doesn't like to admit the fact that she's Minami's aunt considering he is two years older than her, so she asks Mizuki to keep their relation a secret. Mizuki comically asks her whether it must be hard to grow up with very handsome men, and she replies that it is. Rio was a friend of Julia's while she attended Saint Blossom as an exchange student.