Io is first seen in the film during the first scene, explaining the equipment in her father's van and the reason why they were there to Yuki Ichinose. She plays a minor role for most of the film, with her most important role being delivering some disks to her father. Io is in charge of the Godzilla Prediction Network's finances.
Io is quite rude to Yuki Ichinose at first, calling her an imbecile on multiple occasions, and essentially forcing her to join the GPN. But by the end of the film, Io treats Yuki with more respect and the two begin to display a growing friendship when Yuki turns their fleeing car around to save Shinoda. When Yuki was inside a building to be detonated by the miliary, Io pleaded for the explosions to be delayed and lied saying Yuki, who was still inside, was her mother and needed help. Io is willing to lie to the military to gain clearance to enter an off-limits building, however, she does it in the hopes of saving her father before the building explodes. Io does not seem very close to her father, as the two do not talk much to each other when it is not necessary and act more like coworkers than father and daughter. However, when Io reunites with her father in the ruins of the exploded building, she tearfully embraces him, showing that she really does care about him.
In the Manga adaptation, Io is more reserved and quiet. Her mother died when she was very young from illness and birth complications, leaving Io with a depressed view of her parent the Millennian prey on. Yugi however affirms to Io, as she was held captive by the aliens with her father and Yuki trying to free her, that her mother loved her dearly and she'd never want Io so depressed and hopeless.
- In the Manga adaptation of Godzilla 2000 Io sports long pigtails and pale colored hair she got from her mother. She also has more focus than she does in the movie and is arguably the main character with her relationship with her father, late mother, and Yuki more prominent.