According to Greek mythology, Io was the priestess to Hera, wife of Zeus, king of the gods. Zeus took a liking to her, and to avoid detection from his jealous wife, he shrouded the place where he seduced Io with clouds. Naturally, Hera was suspicious of the cloud's formation as well as Zeus' apparent absence from Mount Olympus. When she descended, she found Zeus as a white cloud alongside a beautiful heifer.
Hera knew full well that the heifer was Io, turned by Zeus. To trap him, Hera demanded that Zeus give her the heifer as a present. Zeus had no choice but to present heifer Io to Hera, who assigned the multiple-eyed giant Argus Panoptes as her guard. Zeus sent Hermes to lull Argus to sleep, and he set Io free. Io fled to and made her home in Egypt when she became to be known as the goddess Isis.
As Yukari'sinitial Persona, Io's history and actions mimic Yukari's own: both were saddled with heavy burdens inadvertently caused by their fathers; were severely punished for their fathers' crimes; were abandoned; found themselves at a crossroads in the middle of their journeys but ultimately found it within themselves to continue marching forward and finally fix the problems left for them. Io also shares loose ties to Yukari's ultimate Persona Isis, as she found the answers she needed in Egypt, the birthplace of Isis' mythology. Io was also said to have become Isis after fleeing to Egypt.
The Taurus Zodiac symbol can be seen between the nostrils of the "heifer," indicating Io's association with the constellation. Despite this, Yukari is a Libra.
Io appears as a palette swap for Tomoe in Persona 4 Arena.