Yamato Mizuki is a classmate of Maron, Chiaki, and Miyako, and is the class president. He is also the only grandson of Yamato group that is very rich but he acts as if he is very poor. Because of his gentle, unassuming nature, he doesn't get much respect. He initially has a cruch on Maron, but later he gives up on her. When Miyako and Maron were chatting, Miyako confesses that she has a crush on Chiaki,but she just wants to Maron to be happy.When Maron leaves to find Chiaki,Minazuki pops out from behind a bush crying tears of joy!? The friendship between them to he thought was realy touching! Minazuki confess than he is inlove with Miyako. Miyako was stunned! She angrily pushes him in a lake, thinking he is toying with her. This was no joke! Minazuki tryed to kiss her,then she gives him a whack on the head saying that it would take ten years until she falls for that. At the end of the manga series they are married with a son. In the anime adaptation, He is depicted as being so innocent and pure heart that he is particularly susceptible to demon possession, being one of the few characters to be the target of a possesion numerous times. It is noticable that in the anime adaptation, he's most innocent at the start, while later he becomes more of a nerd comic-relief, becoming Miyako's sidekick in a few cases, although never really doing any contribution.
Numerous times in the anime version there are little bits where Yamato daydreams about dating or doing any romantic activities. These range from sensible ones like him and Maron starting in a commercial, to him imaging himself as Julius Ceasar and Maron as Cleopatra.