Taiyou has blue eyes and blonde hair with two red hairclips on his right. When he is not at work, he usually wears his school uniform which consists of a white dress shirt, a red necktie, black pants and shoes, and a green blazer with a purple, plaid collar. At home, he wears a T-shirt and sweatpants. Many girls consider him attractive.
Before the incident at Princess Imperial, Taiyou was polite and helpful, showing Satou what to do on her first day of work. He was quick to fall for Satou and confessed to her a day later, but got rejected immediately.
After the incident, Taiyou became unstable and paranoid of adult women, trying to publicly maintain the same polite demeanor he had before, but quickly succumbing to his fear when confronted with older women. It wasn't until he stumbled across a missing poster of Shio that he decided to face his fear of older women. Because of Shio's cuteness and young, small stature, Taiyou became obsessed over Shio with the premonition that she could cleanse his soul.
Not much is known about Taiyou's past, but his mother deeply cares for him to the point where Shouko commented that "It would be nice if [Shouko] could have a normal family like [Taiyou's]". When Satou first began to work at Princess Imperial, Taiyou admired her diligence and how she was quick to understand what to do, despite it being her first day of work. He confessed to her the next day, but got rejected almost immediately. Many girls think that he is very good-looking at work, commenting on how they couldn't believe that Satou rejected him and that the person she is with must be far better looking than Taiyou. Out of jealousy towards the attention Satou garnered from Taiyou and other employees, the manager of Princess Imperial coerced Taiyou into her office and raped him, tying him up and taping his mouth shut in her closet for many days. It wasn't until Satou confronted the manager about her low pay and blackmailed her with video evidence of her confessing to raping a minor that Taiyou was finally released.
After being raped by the manager of Princess Imperial, he begins to perceive himself as "dirty" and incapable of being cleansed. Soon however, he encounters a missing poster of Shio, and from then on he became obsessed with her, delegating her as an angel who can cleanse his soul. His obsession intensified after encountering Shio one night in the city, believing that he was slowly becoming pure from Shio's interaction with him, to the point where he wanted to take her home and keep her to himself.
Later on, he discovers that Satou is holding Shio in her apartment and meets with Satou in order to discuss how to get rid of Asahi, incentivized by being able to meet Shio if he successfully gets rid of him. Consequently, he becomes Shio's self-proclaimed "Knight" and tries to deal with Asahi for Shio's sake.
At the end of the anime's closing credits, Taiyo is shown on his knees in his room, defeated and shocked to what has happened. It is never revealed if he gets better or stays like that forever.(in the anime)
Satou and Taiyo were shown to be good friends before Taiyo meets Shio in person. After this, Satou shows no restraint towards him and offers a deal that if he helps her get rid of a threat, she will let him see Shio again. Of course, because of his trauma and obsessive nature he agrees and he becomes a accomplice. In the final epsiode, Taiyo, after being assaulted by Satou's aunt, escaping the fire, calls out for help and for Shio, but Souto ignores him, meaning Souto no longer cared for him.
- Taiyou (太陽) means "Sun" in Japanese. Mitsuboshi mean « Three Stars »
- In the non-canon one-shot series of Happy Sugar Life called "White Sugar Garden, Black Salt Cage", Taiyou bears many similarities in appearance to the character Kiiya, with the only difference between their looks is how their hairclips are positioned (Kiiya is shown having three hairclips on his left, while Taiyou has two hairclips on the right).
- Taiyou's mom wears a very similar set of hairlips.