Mizuno Yuu (水野ゆう) is the Sanrio boy corresponding to the Sanrio character My Melody. Yuu, unlike other Boys such as Hasegawa Kouta, is not afraid to admit his love for Melody -who he proclaims a "Princess" - even in front of the many female colleagues he attracts. He is portrayed as being caring, specifically to the fellow Sanrio Boys and his younger sister. Yuu also appears to have an interest in cooking and baking and seems to be defensive of his friends and their shared interests.

Because Yuu's parents work very late, he is tasked with the house chores and has to look after his younger sister, Yuri. However, he is shown as being a very overprotective big brother and freaks out when Yuri brings home a boy during summer vacation.