Seiji Hiwatari (日渡 星司 Hiwatari Seiji ) Seiji is a member of SHIPS, as well as Kirari's love interest. He is very rich. His parents disagree with him being an idol. Throughout the beginning of the series, he seems oblivious to Kirari's feelings, but by episode 12 he begins to portray feelings of jealousy over Hiroto's and Kirari's friendly relationship. He knows that Kirari and Hiroto love each other and that his feelings towards Kirari are not as deep as Hiroto's feelings towards her. He is gentle and says very encouraging words to Kirari. Since he is as dense as her, he always has a calm and clueless expression. When he is wandering around in the city, he disguises himself as an otaku.
Seiji is the complete opposite of Hiroto. While Hiroto is rude and brutally honset, Seiji is kind and pleasant. He is described as a gentleman by Kirari and others due to his polite manners and kindness. He treats Kirari with kindness and always says encouraging words to her. He is, however, as dense as she is and has a pure innocent heart. Because he is as dense as she is, he always has on a calm, clueless expression and a smile on his face. He considers Kirari and Hiroto as his best friends, but he never fails to declare his true love to Kami-sama, his pet turtle. His love for his pet is so strong thast he gets very angry if something spills on it (ex. soda, acid, or sand). He is oblivious to Kirari's crush on him, but he quickly discovers Kirari and Hiroto's feelings for each other, and is always trying to get them together, even though he expressed jealousy once. Because he loves them both, he wants them to be happy together.
Seiji was born on December 24, 1991 (anime; 1989 in the manga) to a wealthy family. He has one older sister, who is seen in the manga but not in the anime (his sister is never even mentioned in the anime). Ever since he was little, he dreamed of becoming an idol, but his parents disapproved of it and wanted him to marry into another wealthy family. When he was 12, he finally convinced them to let him team up with Hiroto and formed SHIPS. It is unknown when he got Kami-sama, but it was likely sometime after he and Hiroto met.
Seiji is 15-years-old when the series begins. When he first meets Kirari, he is disguised in his usual okatu outfit and wondering around because he had lost Kami-sama. Kirari spots Kami-sama in a tree and rescue it before she accidently falls herself. Seiji catches her and thanks her for saving his pet, and gives her a ticket to SHIPS' next concert. Once Kirari sneaks in to see him, she sees that Seiji, along with Hiroto, are actually SHIPS. Seiji is glad to see her again and asks Hiroto not to be harsh to her. He even approves of her declaration to be an idol and offers to help her.
Seiji has a close relationship with Kirari since he first met her. He likes Kirari because of her cheerfulness and cute appearance, but his feelings towards her are nothing more than a sisterly love. He is oblivious that Kirari had a crush on him, but knew of her feelings for Hiroto and became more involved in helping them get together. While he supports their relationship, he expresses jealousy in episode 12 and even asked her on a date in episode 91. Of all the people Kirari knows, Seiji treats her the nicest. He and Kirari remain good friends after she starts dating Hiroto.
Seiji is best friends and partners with Hiroto. They met when they were 12-years-old and formed SHIPS together. Although they are complete opposites in personalities, they are as close as brothers and rarely argue. Seiji is so close with Hiroto that he says that he will never perform without Hiroto. He supports Hiroto's relationship with Kirari greatly.