|Birthday||July 2 (Cancer)|
|Height||135cm (at 9 years old)
158cm (at 14 years old)
|School||Hama Elementary School
Mihama Middle school
|Manga Debut||Chapter 1|
|Anime Debut||Episode 1|
|Japanese Voice||Kaori Ishihara|
|English Voice||Sarah Anne Williams|
A third grade elementary school girl with light brown pigtails and hazel eyes. She is Miuna's best friend and has a crush on Kaname. After the time skip, she enters high school with Miuna and decides to study hard to become an independent woman, but her crush on Kaname also grows stronger and she tries her best to overcome it. She eventually makes Kaname see her as a girl his age, instead of the little girl he knew before going into hibernation. In the epilogue she is seen with her hair down in order to look more mature, likely as an attempt to impress Kaname.
Sayu has short, light brown wavy hair tied into pigtails. On her right pigtail is a red bow that holds a section of her hair, while just a regular red hair tie on her left. After the timeskip, her light brown hair seems to have grown longer and wears it in small pigtails with red ribbons, and the rest of her hair is open. She has light, hazel-brown eyes, the same color as her hair.
Sayu cares a lot for Miuna. She tries her best to protect Miuna from harm and tries to make her happy. She tries her best at everything so that Kaname would see her as an actual girl instead of just a child. After the timeskip, she becomes a independent and self-confident girl. When Kaname wakes up from hibernation she seems to lose a bit of that confidence, but that's mainly when it comes to him and the topic of romance.
While Sayu has feelings for Kaname, Kaname still has feelings for Chisaki after the timeskip. There is however a growing connection between the two. Sayu tells Kaname that he is selfish to think that it would be better to not love and not consider her feelings. She then tells Miuna that the only reason she could move on with her life was because of her feelings for Kaname and will ask him out, not caring if she gets rejected or not. Probably on her way to do just that, she accidentally sees Kaname eavesdropping on Tsumugu and Chisaki when they were having a private conversation about their feelings for each other. As he walks away she runs after him and confesses that she has always been watching him and that he was always in her heart. Kaname tells Sayu that, when returning from hibernation, he felt lonely and thought that no one had been waiting for him. He then tells her that although he had always been looking at Chisaki, he promised to at least start looking at Sayu now, and see her as a girl his own age.
Miuna is Sayu's best friend ever since second grade. Sayu cares for Miuna as her friend and will do anything to make her smile. The two would fight once in a while about love, but will make up eventually because the two can never break their friendship up.