|Birthday||September 2 (Virgo)|
|Height||4'4 (135 cm) (9 years old)|
5'1 (158 cm) (at 14 years old)
|Eye colour||Light grey-blue|
|Status||Alive | Student|
|School||Hama Elementary (formerly)|
Mihama Middle School
|Family||Itaru Shiodome (Father)|
Miori Shiodome (Mother - Deceased)
Akari Sakishima (Step-mother)
Akira Shiodome (Younger half-brother)
Hikari Sakishima (Step-uncle)
Tomori Sakishima (Step-grandfather)
Hokage Sakishima (Step-grandmother - Deceased)
|Friends/Allies||Sayu Hisanuma (Childhood friend)|
Manaka Mukaido (Close friend after post-timeskip/Senior classmate)
Kaname Isaki (Senior classmate)
Atsushi Minegishi (Classmate)
|Relationships||Hikari Sakishima (Former crush)|
|Manga Debut||Volume 1, Chapter 1|
|Anime Debut||Episode 1: "In Between the Sea and the Land"|
Miuna met Akari Sakishima (Miori's friend) when she visited them shortly after she was born. She loves Akari, but the thought of losing her like she did her mother caused her to refuse to accept Akari as family. Later on, she overcomes her fear and fully accepts Akari as her new mother. She has a crush on Hikari Sakishima. During the five year period of the time skip, Miuna could usually be found staring out at the ocean waiting for Hikari to return. After the time skip, she enters middle school with Sayu Hisanuma. Her feelings for Hikari have only grown stronger, even to the point of rejecting one of her other classmates who has liked her since elementary school. When Miuna falls into the sea by accident, she develops Ena on her skin which allows her to breathe underwater like her mother. In Episode 25, she becomes the Ojoshi-sama, but she is later saved by Hikari.
Before the Timeskip
Miuna is a cute young girl with straight shoulder-length black hair that has a asymmetrical fringe swept to the left side and blue-gray eyes (they appear blue in the light).
After the Timeskip
Miuna has grown her hair out to waist-length and she ties it up in little loops on each side of her head.
She is often seen wearing her Mihama Middle School uniform with long, black stockings.
Miuna is a very shy girl who often relies on Sayu Hisanuma (her best friend) to do the talking. She isn't very direct about her feelings, often using gum to write them on a wall instead of telling them verbally, as a 9-year old. After the timeskip, Miuna is a bit insecure but she is now a smart, kind, bold and independent young middle school student. Miuna cares very much for her mother even though she and her best friend Sayu were shooing Akari Sakishima away ever since she learned of Akari's relationship with her father.
Miori Shiodome (Miuna's biological mother) passed away when Miuna was young (3 years prior to the series), which led to her fear of losing people close to her again. Her mother was from the sea originally, but she was unable to go back after she chose to stay on the surface and marry Itaru Shiodome (Miuna's father).
Soon after Miuna was born, she first met Akari Sakishima soon because Akari was close friends with Miori Shiodome (Miuna's biological mother). Miuna loves Akari, but after Akari and Itaru Shiodome tells Miuna that they want to get married, Miuna begins to worry that she would lose her too like she lost her mother. Miuna tries to reject Akari and writes "Go Away" with gum on the walls of the store that Akari works at.
Eventually Akari decides that she is hurting Miuna by replacing her old mom, so she decides to leave Miuna alone even though she loves her a lot. Miuna then runs away, but Hikari Sakishima and the others all find her by the piers. Miuna loves the sea because her mom was from it, so she jumps into the water wishing that she could swim in the ocean like her mother could. Hikari jumps in to save her and after they surface she tells him about how she doesn't want to lose another mommy. Hikari tells her about all the people he likes, including Miuna now. The following day when Akari finds the two of them, she starts to cry and tells Miuna that while she can't replace her old mom ,she doesn't ever want to leave her.
Miuna develops a crush for Hikari, and later worries about the idea of Hikari going into hibernation. She and Sayu Hisanuma feel that they are "evil" because they would rather have Hikari and Kaname Isaki stay on the surface than go into hibernation where they can be safe. Miuna also worries about Akari, wishing that she too would go to sleep so that she can stay safe. Akari rejects the idea, wanting to stay on the surface with Miuna and Itaru no matter what.
After the time skip, 5 years passes and Miuna often thinks about the sea where Hikari is. She wishes that she could see him again. Miuna is now 14 years old, and goes to the same Junior High School that Hikari went to before. After Hikari wakes up and comes back, Miuna is excited that he's back and that they're now the same age, but she sees that Hikari is still in love with Manaka Mukaido. She is also told by several people that Hikari is her uncle-in-law and that they can't be together, regardless Miuna still has feelings for Hikari, much to their dismay, especially Sayu.
While at the pier with Hikari again like when they were younger, a large crane collapses and causes Miuna to fall into the ocean. As she sinks deeper, she suddenly realizes that she can breath underwater somehow. She comes up with Hikari ecstatic and wanting to tell Akari about it.
The next day, Miuna learned that she has Ena in her skin. She was so excited to hear that she has ena, because she can show Hikari that they are the alike. The next morning, Miuna, Hikari and Kaname go underwater to find the Shioshishio, following a mysterious sound.
Even though Hikari is Miuna's step-uncle, she has feelings for him. She is in love with Hikari, but he does not reciprocate her feelings for him, since he loves Manaka. Knowing this, she does everything she can so that Manaka can get her feelings back for Hikari and holds back her own feelings for the sake of him. She soon becomes the sacrifice in order for them to be together. Miuna doesn't want Hikari to ever find out her feelings for him and tries to forget about them with pain from hearing him say he loves Manaka over and over, hurting herself in the process, but after being the sacrifice, her feelings are exposed after she tells herself that she loves Hikari and falls asleep. Even though Hikari doesn't have any romantic feelings for her, he sees Miuna as a little sister who needs to be protected and he deeply cares about her.
When he learns of her true feelings for him, he becomes conflicted and blames himself for not realizing Miuna's feelings for him sooner, but questions why she would have any feelings for him, and that finding out that him and Manaka feel the same way about each other doesn't matter if it was all just for Miuna to end up like this, so he would give up his feelings of love towards Manaka so Miuna wouldn't have to be the Ojoshi-sama for 5 years. This results in Ojoshi-sama's feelings melting into the sea at Hikari's determination to save Miuna. After the second Ofunehiki, Miuna is able to move past her unrequited feelings for Hikari.
Sayu is Miuna's best friend who have been friends every since second grade when Sayu realizes that she wanted to be dear to Miuna since she was bullied. 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 they will make up eventually because the two can never break their friendship.
After the timeskip, Miuna is the only one with mixed feelings about Manaka. At first, she wanted Manaka to wake up when they found her, but she soon realizes that she doesn't want her to wake up because she wanted Hikari for herself, even unintentionally upsetting Hikari Sakishima when she mentions she hopes Manaka will never wake up, but she realizes her mistake after getting close, she helps Manaka get back her feelings for Hikari and soon becomes the sacrifice to save her. After being rescued by Hikari, she and Manaka acknowledge their friendship.
- The name Miuna means "beautiful" (美) (mi) and "sea, ocean" (海) (una).
- Miuna's surname Shiodome means "tide, ebb, opportunity" (潮) (shio) and "detain, fasten, halt, stop" (留) (tome/dome), which literally means "halt the tides" altogether.