Lu

Lu is the titular deuteragonist of Lu Over the Wall. Lu is a mermaid, who loves to dance and listen to music. Her fins turn into legs whenever she hears music and she is able to freely control water.

Personality
Lu has a very child-like personality, she is easily mesmerized by a lot of things on the surface world and her dream is to make everyone her friend. She is shown to have a love for music and dancing. She speaks in broken english and in the third person.

Appearance
Lu's hair is made of water with three fish that swim around in it. Her skin above her torso appears light-skinned, with the rest of her body being pink, along with pink rosy cheeks. Her arms have noticeable scales on them and she wears a dress made out of seaweed. Lu also has very sharp teeth.

Story
In the film, Lu first appears when Kai Ashimoto is listening to his music, he sees Lu swimming outside his window. Kai turns off his music and run downstairs to see her better, but by the time he gets there, he sees her swimming back to merfolk island.

After Yuho leaves, angry at Kai, Kai and Kunio hear Lu singing and both are amazed by it. Kai goes to find where the singing is coming from and sees Lu dancing on a fence. After the opening title sequence, Lu leaves. Later, when Kai, Yuho and Kunio are being held up by two poachers, Lu uses her magic and lift the two in the air before dropping them, letting the trio escape.

Lu makes her first full appearance in the film, when Kai is playing music. Kai sees her outside his window and throws food to her. Lu rises out and meets Kai face-to-face, she comes into his room, accidentally flooding it. Kai begins to play his music and Lu's fish tail turns into legs. Two introduce each other and Lu gives Kai back his phone (which he had lost to the poachers) before leaving. The next day, during a swim meet, Lu assists Kai by dragging him above the water. Later in the day, Kai introduces Lu to Yuho and Kunio and the four play music together. After arriving back home, Kai sees Lu on land. He tells her to go back to the water, but she insists on coming with him. Kai carries his music box so Lu can walk on land and he spends the rest of the night with Lu, showing her sights, having conversations, and getting to know her. Kai takes Lu to an animal shelter and Lu frees all the dog there and turns them into "merdoggies". She rescues one of the dogs, Wangyo, from the sunlight and adopts him as her own pet.

Lu shows up the next day, outside of Kai's window again, with Wangyo. Lu offers him a boat ride and brings him to Merfolk Island. Lu becomes fascinate by Kai's umbrella. Kai takes a picture of Lu and Wangyo and both get blinded from the flash. Lu brings Kai underwater and brings him to an abandoned ship to see her father. After getting back to the surface, Lu teaches Kai how to float above water.

Kai, Yuho and Kunio bring Lu with them to the Lantern Festival. Lu becomes excited when she sees the lanterns float in the air and forces everyone to dance. Lu dances in front of everyone, but once the music stops she turns back into a mermaid in front of them. Thankfully, Kai and Kunio manage to get her back into the ocean. Later, when Lu visits the trio on the surface, Yuho and Kunio convince her to perform for their band at the grand reopening of Merfolk Land. Lu appears outside the of Kai's school, with Wangyo, trying to get his attention. Lu and Wangyo dance at Merfolk Land for the SEIRÈN's band, however after she realizes the performers aren't her friends, she becomes frightened by the camera flashes and violently splashes everyone on stage and leaves.

Lu makes her way to Kai's house, but is captures by Yuho's father, who is convinced she had something to due with her disappearance.

Kai Ashimoto
Lu and Kai have an incredibly tight bond. After meeting each other for the first time, the two become attached to each other and form a bond reminiscent of a brother and sister. Lu also kisses Kai on the face multiple times throughout the movie and enthusiastically approaches him every time they meet. Near the end of the film, Kai tells Lu that everyone loves her, as well as himself, just like she wanted.

Yuho
Lu and Yuho's relationship blossoms throughout the film. Lu considers Yuho to be one of her closet friends. Lu first meets Yuho during their second visit to Merfolk Island. At first, Yuho is shocked and suspicious of Lu and her identity as one of the merfolk, but quickly begins to take a liking to her. At the grand reopening of Merfolk Land, Lu becomes frightened when she realizes Yuho and the others aren't there with her. Their bond is clearly shown after Lu is released from the giant cage. As Yuho apologizes to Lu, Lu insists that they are still friends, and nuzzles, as well as kisses, Yuho's face, shouting "Yuho! Lu! Friends! Friends!"

Kunio
Lu and Kunio, with their obvious parallels in terms of personality, have a sound relationship. Lu considers Kunio to be one of her closet friends. Kunio's first encounter with Lu was when he heard her singing during band practice and was automatically amazed by it. Lu immediately takes a liking to Kunio when he begins to play music for her and adapt to her singing. Despite being a mermaid, Kunio never seemed to mind and was never phased by that fact, as he was willing to accept her even from the very beginning.

Her father
Lu's love for her father is shown countless times throughout the movie. In the first interaction, Lu (despite seeing her father many times before), seems overjoyed to see her father again. Her father also seems to reciprocate those same feelings, as shown at the end, when he ends up risking his own life to save Lu when he hears she is in danger.

Trivia

 * Lu and her species were originally going to be vampires, before director, Masaaki Yuasa, decided he wanted something cuter.
 * Elements of Lu and species being vampires are still kept in the film, such as their bites turning vampire and animals into their species and being burned when caught in direct sunlight.
 * In the 2019 film Ride Your Wave, which was also directed by Masaaki Yuasa, Lu makes a cameo appearance on an image at the fire station.
 * This isn't the first time Christine Marie Cabanos has voiced a character that comes from the sea. She previously voiced the titular character in Squid Girl.
 * Lu's dress was originally going to be blue, along with her lower half.
 * In the art book Lu has a shark like back fin.
 * Lu’s gills are on her arms, the reason is unknown why.
 * Lu may be older than she seems as she may have possibly bitten Kai’s grandfather’s mother. (Her silhouette was seen in the flashback scene).