|Age||14, 19 (after the time skip)|
|Anime||Between the Sea and the Land|
|Manga||Vol 1 Ch 1|
Chisaki is a beautiful young girl who thought she had developed a little big for her age. With pale skin, long purple hair tied into a pony-tail that hanged on the side of her head. Chisaki looks like an mother that watch over her children as she is sometimes considered 'mother nature' who admires her children greatly. Chisaki has the trade mark sea-blue eyes which would shimmer whenever she looks at Manaka, Hikari, Kaname and Tsumugu. Normally seen in her white and blue uniform, Chisaki likes to travel the surface in summery clothing such as long dresses and sleeveless shirts. After the time skip, it is shown that Chisaki has grown older and understands her surroundings better, having cut her long purple hair to shoulder length and now has a single braid hanging from her left cheek, Chisaki wear long sleeved sweaters and skirts or shorts. Sometimes she is seen in her nurse's uniform.
Chisaki is characterized as somewhat shy, thoughtful, serene, kind, and very polite, as noted from her always addressing people with proper honourifics, the only other times she does not address people with proper honourifics is when she becomes incredibly close to that person. Chisaki does not have much self-confidence. Chisaki's growing self-confidence mainly comes from her long-standing admiration for Hikari, as she was inspired by his enthusiasm and his unyielding determination to never give up no matter what the odds. As the series progressed, her admiration towards him grew into genuine care and affection, eventually she learns that she does not genuinely love him in the sense of a lover, but as a younger brother, this leading her to fall in love with Tsumugu instead. Chisaki also has an unshakeable faith in Hikari and Tsumugu. Chisaki has great pride in being a child of the sea, but gives it up as she learns she loves the surface more. Being independent and eventually growing a little tough, she does not like people helping her. Chisaki takes pride in her skills and never lets anybody down. She works her hardest for her beloved friends seen as she gives Manaka encouragement and continuously shows support towards her to matter what and greatly wishes Manaka to return Hikari's feelings. Chisaki's loyalty and devotion towards her closest friends were seen time and time again, feeling protective towards all of them. Despite all this, Chisaki also feels incredibly grief-stricken as Manaka was used to save everyone and wishes to take her place so Manaka can live a normal life, but realized that so many people need her and Manaka would never forgive if she did so. One of her faults is dashing into things recklessly.
When Manaka 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, and the feeling of him holding her hand caused her to have feelings for him. As a child Chisaki had been a bit selfish but had grown out of it as she had gotten older, when she was a child she got upset greatly at Manaka for accidently missing a special meeting the four was supposed to have. This surprised Manaka and she started to cry. Chisaki is an only child with a loving mother and father, both are strict but learns to let her go and make her own plans and such. It is shown, Chisaki had always wished to become a nurse but never thought she would be able to become one until Tsumugu's grandfather got terribly ill.
Through the series Chisaki plays a Mother like Role as stated by Hikari, Chisaki is Manaka's best friend, she has a difficult role as Manaka always comes to her for help or whenever something bad happens.
Former student of Nami Junior High School, Chisaki is forced to attend a school on land called Mihama Junior High School.Chisaki isn't exactly on the sidelines like Kaname as she is needed more. Being the reasonable and head leveled one, Chisaki acts as the mother of the group. Looking out for everyone and doing her best to make everyone happy. Despite having a jealous and selfish strike within her, Chisaki is well loved person. During the series, she over comes tough hardships such as Manaka overhearing her telling Tsumugu about her feelings. Kaname's confession and more. Chisaki doesn't want things to change so when Manaka shows interest in Tsumugu, she is upset when Tsumugu seems to return Manaka's feelings. Even going as fair as to whisper, "Don't be so kind to Manaka anymore. She has Hikari." At this time, she really hates Tsumugu and the surface, hating the fact the group had to go up to the surface, Chisaki discovers Tsumugu is making a watering hole but wishes Tsumugu wasn't so nice. Playing the 'big' friend, Chisaki is always weary about showing herself. She gets teased about this a lot as in one episode one of her 'surface' friends grab hold of her breasts and comments on how big they are. During this time, she gets ashamed as once again Manaka stood up for Hikari ahead of her, to the point of refusing to help taking him to the infirmary. When the group goes of into town with Miuna, Chisaki is once again confronted with her feelings as in one of the stores, Chisaki and Hikari get left behind since the elevator was full. Chisaki uses this moment to discuss with Hikari his feelings for Manaka. Hikari claims that if Manaka chooses to be with Tsumugu, he will respect that.
At the very beginning it is shown that her and Kaname are very close, they spend so much time together talking about their problems. She is surprised when Kaname confesses to her. She is so shocked and overcome with guilt for not noticing and always coming to him with her problems, that she brushes it off. Completely ignoring it and acting like nothing had happen.
Before the hibernation, Kaname pushes Hikari to confess to Manaka and when she runs off, he chase after her. Chisaki breaks down and runs after him, telling him not to follow her. She confesses to him and admits she'll never win against Manaka. The next day, Chisaki is on the boat with Kaname for the festival. Wishing the sea-god would allow everyone to stay together when suddenly, the boats are surrounded by whirlpools and both Akari and Tsumugu fall at the sea and are pulled down. Chisaki cries out for Tsumugu and dives in and Kaname follows after to her. Kaname helps Chisaki get Tsumugu onto the boat. The boat carrying Kaname, Chisaki and Tsumugu makes a fast maneuver to avoid a pillar falling onto them, but Kaname falls in the occasion. Seeing this Chisaki screams at the top of her lungs, without being able to do anything. Once every calms, Chisaki his heart broken as she realizes the others hadn't come up. She soon sees, that she is the only one to not hibernate. This leaves her broken. While the people are on the surface, deciding what to do. She sits in the corner, just staring at nothing. Blaming herself for Kaname and not being able to help him. When the surface people began to question what they'll do with her, Tsumugu's grandfather states they'll take her. With a lot of effort, Tsumugu is able to make her smile again. Both grows close as they mourn their friends sleeping and being unable to prevent it. As time progresses, Chisaki goes into high school and then college, before deciding to become a nurse as Tsumugu's grandfather falls ill. When he's being carted into the hospital, she is devastated and screams to the sea-god not to take anybody else from her.
Five years later, the sea over Shioshishio is frozen and the surface enters into a continued winter. Chisaki pays a visit to Tsumugu's grandfather Isamu at the hospital before returning to meet Akari and her son, Akira. Chisaki learns of Hikari's return but refrains from meeting him in fear that she has changed to much. She had been the one who didn't want things to change and yet she is the one. She feels she is the one who was left behind. She confesses to Tsumugu that she is afraid of how Hikari will react upon seeing her and later that day, she accidently meets Hikari again who admits to her she hasn't changed at all.
- Main article: Chisaki Hiraidaira/Relationships
- "I have to save her! Manaka doesn't have Ena!"
– Chisaki after Manaka falls of the boat
- "Enough Manaka! You missed it! I can't believe you! It was supposed to be all of us!"
– Chisaki as a child, after Manaka zooming out a missing the salt festival
- "Manaka...she had loved Hikari all along..."
– Chisaki finding out about Manaka's feelings
- "I hate you! You're changing everything! I don't want it to change!"
– Chisaki to Tsumugu. Getting frustrated that Manaka may love Tsumugu
- "Stop...Stop being so nice to Manaka...she has...Hikari"
– Chisaki thinking about Tsumgu
- "Stop...Stop...No...No...I...I can't be the only one happy."
– Chisaki after Tsumugu holds her. Both tell eachother they love eachother very much
- "Then you shouldn’t have volunteered. "
– Chisaki teasing Hikari as they create the wood puppet
- "For someone on the surface to care so much about the village…Isn’t that great..."
– Chisaki to Kaname about Tsumugu
- "Yeah, if it spits up a black rock, your feelings are wrong, and if it spits up a pretty rock."
– Chisaki to Manaka about the sea slug
- "I was so worried...that everyone had changed...but...it was me...who had changed...."
– Chisaki sobbing to Tsumugu
- Chisaki had only loved Hikari has a brother as she learn she had been in love with Tsumugu all along.
- Chisaki's favorite color is purple.
- She is ranked as second favorite female of the show.
- Chisaki shares a theme song with Tsumugu called Heart That slips through.
- Chisaki plays a mother like role to Manaka and Hikari the father as stated by Hikari in the anime.
- Chisaki was the only that escaped Hibernation with her friends
- Chisak is the only one shown as an adult
- Main article: Chisaki Hiradaira/Image gallery