Mizuki is a second year student of Eiden school. Her grades aren't too well though. Mizuki is a skilled swimmer who attained second place in the junior high swimming competition. She joined the swimming club to swim in their pool, but later dropped out because she dislikes competition. She chooses to study at the all girl Eiden school for the freedom to swim in the sea.
Mizuki talks very fast when she is nervous or excited. There is a running gag where Kazushi could see her exposed multiple times. She gets infuriated and calls him "Bakazushi".
Mizuki is tomboyish and does not display interest in boys. Because of that, many girls assumed that she was lesbian. When confronted about it, she becomes angry and insists that she is straight. Kazushi and Mei also witnessed a girl expressing her feelings for Mizuki. Mizuki explains that she is straight but the girl remains unshaken. Mizuki then ran away with the girl giving chase.
Early in the game, Kazushi saw her swimming naked in the sea. He mistakes her for a mermaid and had mostly forgotten her face. Mizuki remembers it though, and she remains cold and suspicious of Kazushi. Later when Kazushi sees her swimming in the school's pool, he remembers it. Mizuki tells him to forget the incident and teaches him to swim in return.
On Mizuki's path, Daigo was given a birthday celebration. Mizuki was asked if she has a boyfriend yet, and she used Kazushi as her excuse. Eventually she developed feelings for him. Mizuki decided to stay away from Kazushi to explore her feelings. Rin explained to Kazushi to take the initiative to approach her. Mizuki revealed that her dream is to swim with the dolphins in the sea surrounding Eiden island. Kazushi and Mizuki later discover a pair of dolphins and they swam with them.
When Mizuki and Kazushi visited Miya's shop in the downtown area of the island, they found a necklace with a beautiful stone. Mizuki expressed her desire to own the necklace, but Kazushi was shocked by the price tag. He bought the necklace by installments.
Later, Kazushi and Mizuki discovered that a dolphin was trapped by a boat in a stormy weather and it was about to be crushed. Kazushi and his three friends saved the dolphin, but he fell into the sea. Mizuki then saved him but the waves swept the boat and crushed her legs. She was hospitalized and the Miya diagnosed her and explained that she may not be able to use her legs again.
Mizuki fell into depression and lashes out at her friends. Kazushi swore to study alchemy to heal her legs. Mei explained that they would require the Nobleman's Stone that was hidden somewhere on the island. The Principal revealed that she was also in search of the stone for her own purpose and she threatened to take his life. Mizuki then shows up to defend Kazushi.
The Principal then realizes the value of human relationship and shed tears which coagulated into the Noblemen's Stone. She gave up the stone to Kazushi and he used the stone to further his research to heal Mizuki's legs.
Edelweiss Eiden Fantasia
On Sakura's path, Mizuki and Ran suspected Sakura's strategy of giving Kazushi the cold shoulder to attract his attention. After Sakura was admitted to the nurse's office, she discovered the black marble that was created from Kazushi's and Sakura's alchemy experiment and presented it to Rin.