Prince of the Frog Kingdom. He cast the frog spell on Aoi, it seems, just on a whim. Often seen with his flying horse, Hidenori.

Aoi, a regular boy, is cused with a spell that turns him into a frog whenever he gets wet. He is sent to another world with a frog kingdom to find the princess to undo the spell. When he finds out that she doesn't know how to lift the curse, they set out to find the spell that will. Along the way they meet many interesting creatures, come accross many dangers, and make many new friends.
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(Source: Anime News Network)

Mizuki Sano graduated from Fujinomiya West High School, and Shizuoka University with a degree in law. He has a younger brother, Daiki Sano, who is also an actor. The two main characters in the manga Hanazakari no Kimitachi e are named after him.

Mizuki Sano joined Johnny's in 1991. In 1993, he became a member of the short-lived Johnny's unit J-Eleven and also a member of KinKi Jr., a backup group for KinKi Kids. In 1995, Sano became a first-generation member of Johnny's Sr., along with Masayuki Sakamoto, Hiroshi Nagano, and Yoshihiko Inohara of V6. Until 1996 he was a backup dancer for Hikaru Genji, V6, SMAP, and KinKi Kids. 

Unlike most of his contemporaries in Johnny's, Sano has neither graduated from Junior status nor left the management of Johnny's. He now mainly performs as a stage actor.

"Aoi was an ordinary boy until a wizard from the Land of Frogs, Makaeru, splashed magical water over him, turning Aoi into a frog. Makaeru then throws Aoi into a tree trunk, transporting him to the Land of Frogs. He is found by Princess Mimori, Makaeru's sister, and together they go on a quest to find the missing pages of the Magic Book that can remove Aoi's curse. For you see, when Aoi gets wet, he turns into a frog, and when he is dry, he turns back into a human..." (From T.H.E.M.)