Masahiro Hamasaki is a supporting character who appears in the second season of the anime, Mermaid Melody Pichi Pichi Pitch Pure, and earlier in the original manga. He is a flirtatious and rebellious teenage boy with short green hair and green eyes. He attends an elite school located next to the school of Rina Tōin, Luchia Nanami, and Hanon Hōshō. Masahiro comes from a wealthy background as the successor to the Hamasaki conglomerate, a large business family. In the anime, he struggles with the pressure of the predetermined future expected of him, finding escape in activities such as riding a motorcycle and practicing amateur boxing. In the manga, his connection to the mermaid world is deeper: his ancestor built a shrine dedicated to mermaids, and he eventually comes to feel he is a descendant of that ancestor and a mermaid, which influences his bond with Rina.

Masahiro’s personality is described as calm and mature, though he often displays a flirtatious and somewhat rebellious exterior. His core motivation is his growing affection for Rina Tōin, one of the mermaid princesses. Initially, his feelings are those of a crush, but over time they develop into genuine love. He pursues her persistently, and their relationship evolves from friendship to romance, culminating in them becoming a couple by the end of the story. Masahiro also interacts with other characters, notably teaching Nagisa Shirai how to ride a motorcycle. He shows a protective side toward Rina, especially as the conflict involving the mermaids and their enemies intensifies.

His role in the story is that of a human ally and love interest for Rina. While he does not possess magical abilities, his physical skills are notable: he is a capable amateur boxer and a skilled motorcycle rider. These abilities occasionally aid the main characters in practical ways, such as transportation or physical confrontation. Masahiro’s development centers on accepting his feelings for Rina and finding his own path outside the expectations of his family, ultimately choosing a life connected to her and the mermaid world.