In the Fringes of Gyr Abania, south of Rhalgr's Reach, there is an enormous hole known as The Yawn. A Chocobo known as Alpha leads the Adventurers, Cid, and Nero back to The Yawn. Originally it was empty, but when they arrive, they find it is filled with a strange light purple liquid.
After descending into the liquid, they find themselves within the Interdimensional Rift. They are greeted by Omega, which the Adventurers and Cid had reactivated to fight Shinryu. Omega relays to them that it created Alpha to lead strong beings into the Rift. It designates them as the Alpha group and explains it is performing an experiment. It pits some of the strongest fighters throughout the different dimensions and stars against one-another to determine who is strongest. Omega's end goal is to return to its home star, but in order to do so, it must evolve by fighting against the strongest.
The Interdimensional Rift is filled with many egg-shaped constructs with a large screen. Each one contains an arena, with the screen available as some sort of label. Omega has monitors called "Level Checkers" which he uses to personally examine each fight as its occurring and to test and eliminate the weaker fighters.
There are three segments to the Interdimensional Rift known as the Deltascape, Sigmascape, and Alphascape. Deltascape is sourced from Planet R and Sigmascape is sourced from the World of Ruin. As the Alpha group proceeds between the segments, Omega demonstrates its ability to modify the Rift. It removes the unnecessary constructs and makes slight changes to the appearance of the Rift. After Omega's defeat in Alphascape V3.0, he deletes the Rift entirely in an effort to destroy Alpha group, minus Alpha himself. All that is left is the Void. This attempt fails as Alpha is able to successfully hide Cid and the Adventurers by shrinking them with a shrinking effect card. The adventurers confront Omega while Alpha rests and Cid keeps him safe.
The background music of the Interdimensional Rift is "Deltascape", an arrangement of "The Prelude of Empty Skies" from Final Fantasy V.
Behind the scenes
The encounters in the Omega raids comprise of bosses from previous titles in the series. Deltascape features bosses from Final Fantasy V, Sigmascape features bosses from Final Fantasy VI, and Alphascape V1.0 features Chaos from the original Final Fantasy.