Io Castle is the home of Princess Jupiter, and it was given to her by Queen Serenity when she was born. It orbited around the planet Jupiter, and only appeared in the manga.

In Act 48, the Solar System Senshi called upon the power of their castles and directed it to the Holy Grail, which gave Sailor Moon the power to transform into Eternal Sailor Moon.


Io is one of the largest moons in Jupiter, the other ones are, Europa, Ganymede, and Callisto.

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