BioPonyo was a goldfish and one of the many the fish-like daughters belonging to Fujimoto and Gran Mamare. One day she swims away from her father's ship and meets Sosuke. She licks his finger where he cut himself breaking open the glass bottle she was trapped in. Soon after his cut heals, Sosuke names the fish Ponyo and she takes a particular shine to him. When Fujimoto takes her back to his ship she refuses to comply to his rules and starts to use magic to transform herself into a human girl. She only partially transforms into a girl before Fujimoto reverts her transformation. Later her sisters help her escape and she finally gets to the surface and turns into a little girl. While out of water she can peform magic, but it does exhaust and partially revert her for a time.
As Sosuke's town is thrown into a tsunami she helps Lisa, Sosuke, and many others to get through it, mostly by using her magic. Later when she meets with her mother and is asked if she wants to beome a human, she agrees to give up magic to be with Sosuke. She is then placed in the care of Lisa and Koichi and eventually turns back into a girl when Sosuke kisses the bubble she was placed in.
In "Mystery Case Files: The Fanfiction" she is one of the orphans at the orphanage that Emmy used to live in. She was then taken by Hansel and Gretel along with Lotso and Stayne before the forming MCF rescue them.
- She is very simular to Ariel from "the Little Mermaid"
- Both fall in love with a human whom their fathers despise at first(Eric, Sosuke)
- Both defy their fathers and turn into a human anyway.
- Both are curious of their love interests' other world above the sea.
- Both are turned back into their respected forms in a certain amount of days
- Both have a maximum amount of siblings(Ariel had 6 sisters, while Ponyo had many other sisters)
- Both decide to stay with their love interests in their world with parents' consent at the end
- However, the major differences are the forms(Ariel was a mermaid, Ponyo was a fish), their ages(Ponyo is 5 while Ariel was 16), they turn into humans different ways(Ariel: Going to Ursula the Sea Witch and trading her voice, Ponyo by licking Sosuke's blood and 'sprouting' her human form), their love interests have a hard time reconizing them after first meeting(albiet Sosuke reconized her immediately while Eric had to remember in 3 days that she was the girl who saved his life).
- It is unknown if she'll return in a future story.
- Mystery Case Files: The Fanfiction(Debut; episode: Meet Emmy or "The First Mystery")