Masato first meets Nanami in their classroom on the first day of classes when he saves her from Natsuki, but he has already seen her before at the park singing with a group of children. Before Masato entered Saotome Academy, it was through Nanami that he found his desire and passion for music and a goal to pursue a dream of becoming an idol. It is also implied that he had been in love with her ever since that snowy day, but tried to ignore it because he believed that he would never see her again. Upon formerly meeting her at Saotome Academy, he recognized her instantly, but did not say anything, instead choosing to observe her and see what kind of person she was. When Haruka has trouble playing in front of their class, Masato helps her get over her fear, and also realizes that she is overall, a good person. He is one of the six people to ask for her as his composer for the graduation audition. It is shown that he has romantic feelings for her. In chapter 4 of the manga they almost kiss, but Haruka stopped them before it happened since they would be expelled.
As the series progresses, Masato's feelings for Haruka continue to grow and deepen, to the point where he even says in Episode 1 of Season 3 that he is "flooded with feelings of love." It is also implied that he dreams of Haruka, or at least fantasizes over her, when he says in the same episode that he thought she was "an illusion of the passions in his heart," and not really there. He gets easily jealous whenever another man, especially Ren, attempts to get close to her, or says something suggestive towards her. When Cecil first appears in Season 2 and kisses Haruka's hand, Masato, along with the rest of STARISH, gets extremely jealous, and when he attempts to kiss her, Masato and the rest of STARISH charge up to them in a fit a jealous rage. While Syo, Ren, Otoya, and Natsuki separate them and hold Cecil back, Masato shields Haruka with Tokiya. He later trades with Ren and holds Cecil back once he attempts to kiss her again.
In Season 4 Episode 1, Masato appears when STARISH pull Haruka away from QUARTET NIGHT and onto their plane. He then holds her as if they were dancing, saying that he, "wants her to accept his overflowing feelings."
A childhood friend and Masato's rival. They first met each other at a social gathering when they were kids, and it was Ren who invited Masato to play with him at the lake because he said the party was boring. As years passed by, Masato soon realizes that the Jinguji group and Hijirikawa group are rivals, and thus he wasn't allowed to meet with Ren anymore. They soon meet again at Saotome Academy, and even share a room together. Masato envied the fact that Ren was free in his family business while he was restricted. After the debut of STARISH, Ren became his partner and rival in the business world.
Masato's classmate in the A class and fellow group member in STARISH. Their relationship between one another seems to be on good terms.
Also one of Masato's classmates in the A class and fellow group member in STARISH. His relationship with Otoya is a friendly one, since Otoya was also the person who gave him the nickname "Masa". Both their feelings are pretty mutual since both have not been caught fighting.
In the Shuffle Unit CD 'Beautiful Love', it is revealed that Masato and Syo are actually fairly close. They agree that both are serious, worry too much, and are wrapped around their roomate's fingers. They bonded especially while at school together, when Natsuki's cooking would often leave Syo without dinner. Seeing him hungry, Masato would often offer Syo whatever food he had in his room, usually rice balls. They stayed fairly close after that, as a 'bond through the stomach.'
A fellow member of STARISH. The two get along very well, due to similarities in personality. Often seen talking to one another.