Sea of Data

The Sea of Data (データの海) refers to the massive collection of unused data in The World and all derivative games. "Deleted" or discarded data is all broken up and returned, inactive, to the sea. Aside from this, little is understood about it.

End of The World
After their defeat at the hands of Kite and the .hackers, all of the Phases except for Macha fell into the Sea of Data. As part of the R.A. Plan, Jyotaro Amagi and Jun Bansyoya searched through the Sea and recovered the Phases' data.

.hack//G.U.
After using the power of Rebirth, Ovan falls into the Sea of Data. There he encounters Aura, who disappeared into the Sea after leaving "The World".