Callisto is a character in SolarBalls, who is one of the Galilean moons along with Io, Europa, and Ganymede She is similar to Eris in character, being unamused, and melancholic. She is also similar in appearance, in which she has dark rings around her eyes. She is also annoyed easily, particularly with Io due to his tendency to eject sulfur dioxide randomly and how he jumps to conclusions.