Gigi is an elderly turtle inhabiting an island visited by Shimajiro and his friends on their underwater journey. This character aids the group by treating an injured baby whale's fin, displaying expertise in marine life care. Gigi hosts a pop quiz show that Shimajiro passes, playing a key role in the whale's recovery.

When three fish ladies voice their dislike for whales, Gigi passionately challenges them, successfully convincing them to support Shimajiro's mission. This action underscores Gigi's protective advocacy for whales and sway within the ocean community.

The character's core function involves enabling the baby whale's reunion with its mother, actively contributing to the rescue alongside Shimajiro's group. Information regarding Gigi's presence or development in other Shimajirō media is limited to this film.