|Birthday||July 3 (cancer)|
|School||Mihama Middle School
(Namiji before it closed down)
|Manga Debut||Chapter 1|
|Anime Debut||Episode 1|
|Japanese Voice||Ai Kayano|
|English Voice||Brianna Knickerbocker|
She is secretly in love with Hikari but she hides her feelings due to the fact that he is in love with Manaka. Chisaki is afraid it will ruin their relationships and hides her feelings. Chisaki is the only person among her Shioshishio friends who avoids hibernation after the Ofunehiki festival. Since the Ofunehiki festival, she has been staying with the Kihara family and also studying in a nursing school. When she reunites with her Shioshishio friends, she feels left out as she is now much older than them. Chisaki fears change, and feels guilty for having lived a relatively happy life during the time skip despite the absence of her friends. She has been pretending to have her "old feelings for Hikari as a means of claiming she hasn't changed over the past five years", but she is really in love with Tsumugu Kihara. They then become a couple. In the last scene, she still continues to live in the Kihara residence with a now-healthy Isamu Kihara, while Tsumugu is away for college.
Chisaki is a beautiful young woman but has a complex about her "oversized" body. Before the time skip, she has long, wavy purple hair that she usually wears in a high-side ponytail on the left side, aside from two thick locks of hair next to both sides of her face that reach her shoulders. She has short bangs that hang to her eyebrows. Chisaki has fair skin and her eyes are blue like all the people from the sea. To her embarrassment, she is commonly described as curvaceous and she usually gets attention from boys because of it. Before the timeskip, Chisaki is usually seen wearing her school uniform, but wears other clothes from time to time, too, like long skirts and blouses. Chisaki wears her uniform with a pair of white crew socks with blue rims and decorates her ponytail with a cornflower blue scrunchie-style hair tie with an attached pair of dark blue ribbons.
After the timeskip, Chisaki becomes taller and more curvaceous. She also cuts her hair to shoulder-length and is slightly wavier than it was before the timeskip. She wears it down with a small side braid tied with tiny blue bows on the right side. She usually wears casual sweaters and denim shorts and skirts with thigh-high socks. She is occasionally seen in a pale purple pajama set, which she sometimes wears loose twin tails with. Sometimes she is seen in her nurse uniform. She also seems to prefer high top shoes.
Chisaki is a kind, cheerful and mature girl who cares a lot about people she loves. She doesn't want to let her friends change because she fears that if her friends change, their relationship would become different. Despite her usually non-violent nature, she can have the angry and annoyed outburst. She is very calm about situations too.
When Manaka Mukaido and Chisaki were kids, there was one time they got lost. They had gone to the outskirts of the village into the outer sea to look for coral. Unable to find home, the two were saved by Hikari Sakishima and the feeling of him holding her hand caused her to have develop feelings for him.
On their first day of going to school on the surface, Chisaki walks with Kaname Isaki and Manaka Mukaido who greets Hikari Sakishima just as he arrives and runs past her. Seeing him berate Manaka for wearing the uniform of the surface school rather than that of their underwater school, Chisaki gets between the two of them and tells him to leave her alone. Manaka decides to change, leaving Chisaki and the boys to go on. As they arrive at the surface, Chisaki leaves with Kaname for school but on the way they see that Manaka has been caught up by mistake in the net of a fishing trawler.
At school, Chisaki takes part in introductions in the morning before having to break up another argument between Hikari and Manaka. Later, giving her P.E. clothes to Manaka to help her stand out less, telling her she has no use for them and advising her that Hikari truly cares for her. The two girls then look out the window at the running track and spot Hikari racing Tsumugu Kihara, quickly losing his footing and knocking both of them down.
The next morning, before school, Chisaki and the group arrive to pick up Manaka from her house but find that she refuses to come out, forcing Hikari to go get her. At school, a group of girls take Manaka into the sun to inspect her supposedly shining skin. Chisaki attempts to stop them but is unable to do so as Manaka is quickly embarrassed and makes a run for it. Notifying Hikari and Kaname, the three go looking for her.
Looking through the city, Chisaki and the group come to the conclusion that Manaka did not return home. As they notice their skin beginning to crack from sun exposure, the three take refuge in the water temporarily, before Hikari leaves to continue the search alone. As Chisaki begins worrying about him, Kaname comments that she and Hikari look like parents to Manaka and tells her if anything happens to Manaka, she will be next to his side. This upsets Chisaki as she tells him that he's not funny, adding that she loves Manaka and does not want anything to happen to her.
At the beginning, Chisaki disliked Tsumugu because Manaka seemed to be in love with him and she feared that this would cause the group to "change" by drifting apart. However, after interacting with him and coming to an understanding, the two become much closer, so much so that she dives into the ocean to save him after his boat is capsized by a large wave from the Sea God during the Maiden Sacrifice. She proceeds to save him with the assistance of Kaname, cradling him in her arms once he is safe.
Years after the freezing of the sea, their relationship has developed. They are now living together and seem to have a special bond, seeming to understand each other on a more personal level and are shown to perform household tasks in sync with one another, much to the ire of Kaname who begins to feel jealous of this new bond. After the 5 years they spent together Tsumugu admits to Kaname that he is in love with Chisaki. He even thought it would be better if Manaka, Hikari, and Kaname didn't wake up because he was scared that Chisaki would disappear from him. After overhearing an argument between Hikari and Tsumugu she discovers that he is in love with her, shocked she jumps into the sea where he tries to follow. After following her he confesses his feelings for Chisaki and tells her that she was like the beautiful sea. Chisaki rejects his confession and cries that she is not in love with him. When walking back home, Chisaki admits her feelings for Tsumugu by lamenting about how quickly she fell in love with him, after only being together for five years, in comparison to having been with Hikari and the other since they were born. Kaname helps Chisaki realize her true feelings though Chisaki believes she isn't allowed to love Tsumugu due to her loyalty to Manaka, whom she thinks has feelings for Tsumugu. Chisaki also thinks that by admiting her love for Tsumugu, she would be betraying everyone that was still sleeping. Chisaki insists to Kaname that she is in love with Hikari no matter what. She also believes that she can't accept Tsumugu's feelings since Tsumugu is needed in order to awaken Manaka's "feelings of love" for him. Tsumugu revealed that Manaka was in love with Hikari to Chisaki which leaves Chisaki happy but still conflicted as she believes she shouldn't be the only one out of her friends to achieve happiness. After the second Ofunehiki, the two become a couple.
Chisaki is the best friend of Manaka, and they were always together in the past. Chisaki helps and protects Manaka, because she doesn't want Manaka to change, in fear of the group going their separate ways. Also it is very hard for Chisaki to be with Manaka, because Chisaki has strong feelings for Hikari although he loves Manaka. She can't accept Tsumugu's feelings because she thinks Manaka is in love with him. But, Manaka is in love with Hikari and the only reason she kept it from everybody was because she thought it would make Chisaki sad.
Early in the series, Chisaki has a crush on Hikari, who is also one of her childhood friends. She admires his ability to change those around him and his will to fight and stand up for himself and others. After the time skip, she has gotten over him, but she doesn't want to change so she tries to make herself like him again. She made sure that she wouldn't forget that she was in love with him. When Hikari told her that she didn't change, she was so happy. Soon, she finds out that he and Manaka are in love and realizes her feelings for Tsumugu.
Kaname and Chisaki have been good friends since they were kids. They often look after each other, and Kaname has a crush on Chisaki, although he knows about Chisaki's feelings towards Hikari. When Kaname confessed to Chisaki, Chisaki was surprised and didn't know how to act when she was with him. He even said after he wakes up from the hibernation his feelings for Chisaki won't change. After the time-skip Kaname moves in with Tsumugu and Chisaki and he appears to get jealous whenever he sees Tsumugu and Chisaki together, meaning he still has feelings for her. But he helps Tsumugu by telling the truth about Chisaki's feelings so that Tsumugu and Chisaki can be together while he moves on. Meanwhile, he might become Sayu's potential future partner, considering she has had strong feelings for him for years.
- The name Chisaki means "A thousand blossoms".