Choa Shin

Choa Shin is the main female protagonist of the series that is a mermaid borrowing human legs as a result of not being able to swim. She then took lessons from Soo and also close friends with him along with Woo.

Appearance
Choa has two different appearances for her two forms. When she is human, she has long brown hair that reaches the middle of her back and dark blue eyes. She also has bangs that are mostly swept to her left of her face. When she is a mermaid, her hair is blonde and her eyes are a much lighter and brighter shade of blue. Her tail is also light blue and the same color as her eyes.

Choa is usually seen wearing her school uniform, which consists of a short, black, pleated skirt, a white collared shirt with a beige sweater on top, and a black ribbon that is tied around the collar. She occasionally wears a jacket on top of her uniform. When Choa is having her swimming lesson, she wears a light blue swimsuit designed like a skirt. She always wears a bracelet with a light blue stone/bead.

Personality
Choa is rather caring, especially for her family. Choa is also very hard-working and persistent, especially when it comes to swimming. She seems to think very realistically and prefers being alone (shown because of how distant she is towards her classmates and how she prefers eating lunch alone). Choa has insecurities because of how she is unable to swim even though she is a mermaid.

Towards her classmates, Choa seems very distant. One classmate, Harim, says to Icelyn Lee that she's not sure whether Choa is too nervous or doesn't want to be close to the others, but something about her is hard to approach. However, she also says that Choa is nice and helps her with math problems.

History
Choa was born a mermaid and lived with her mother and sisters in the sea. However her tail was weak so she was unable to swim, no matter how much she practiced with her sisters. Choa heard other mermaids gossiping about her, causing her to have insecurities. Choa and her family went to a witch and asked her for human legs so that Choa could live more easily with her father on land. The witch said that Choa was too young for permanent human legs and offered "incomplete" legs instead, which allowed her to be a mermaid in water and a human on land. (These legs would only last until she became an adult.) Choa started living with her human father with these "incomplete" human legs.

When Choa became human, she ran around a lot to try to make good use of her legs. She was very wild and chased her Woo Seon around with a frog and even bit him once.

She has not visited her family or the ocean for a very long time. The reason is unknown.

Episode 1
Choa attends a swim meet, where Soo Lee recognizes her. Later, he asks her if she was there, and she says yes. Soo says "you must love swimming too", to which Choa replies that she doesn't like water. Later that day, a teacher asks Choa to give something to the swimming coach. She does the job and stops by the swimming pool to reminisce. Soo surprises her and she falls in, revealing her mermaid appearance.

Episode 2
Choa confirms that she is, indeed, a mermaid.

Episode 5
Soo tries to convince Choa to learn swimming from him, and after awhile, she finally gives in.

Episode 8
Choa gets caught coming out of the swimming pool with Soo by Icelyn Lee and Chan Song, Soo's two friends. Icelyn and Chan (but especially Icelyn) misunderstand and think that the two are dating. Choa manages to escape the situation quickly and has a talk with her father. It's revealed that Choa hasn't gone to the ocean or reunited with her family for a very long time, although the reason is unknown.

Soo Lee
At first, Choa was very distant from Soo. Initially after he finds out she's a mermaid, she is very icy and threatening towards him. Later, he starts teaching her how to swim and she states that she is very glad to have met him, thinking he is quite reliable for that. She may have also developed feelings for him through certain moments, though she thought it was a mere misunderstanding at first, and she would get quite awkward around him whenever those moments play out between them. This may also be due to the fact that Choa would be returning to the ocean soon, and she didn't want them to get too close, otherwise Soo would miss her.

Woo Seon
Choa and Woo are childhood friends. When Woo appeared again after several years at her school, Choa was suspicious of him at first and didn't know who he was. However, she warmed up to him again after he told her they were childhood friends and he proved to be trustworthy. They also reminisced about their childhood memories, and Choa was embarrassed by her behavior, though Woo thought it was fine. Choa also thought Woo was reliable since she could tell him everything about what's going on with her. And whenever Woo would show a certain amount of affection towards her, Choa would try not to overthink it, and simply conclude that they are friends and nothing more. Choa would get worried about Woo whenever he felt down, too.

Icelyn Lee
Icelyn was very suspicious of Choa and thought that she is dating Soo Lee. Choa seems to just think of her as Soo's friend but does think that it's strange that Icelyn keeps staring at her or observing her.

Chan Song
Chan has a small suspicion that Choa and Soo are dating but otherwise doesn't seem to have much of an opinion of her. Likewise, Choa doesn't seem to have much of an opinion of Chan. Still, Choa accepted "Chan"'s invitation to accompany them to the swimming competition to cheer for Soo. Choa also got weirded out by him later when he was excessively winking at her, attempting to convey his message.

Harim
Harim seems to be the only classmate besides Soo who Choa is remotely close with. She often tries to include Choa by asking her if they wanted to eat together or being her partner in an activity. She says that even though Choa is rather hard to approach, she is very nice and helps her with math problems.