Void Gauntlet

This place is accessed through the Hyperspace Hole in the Crystal Cave. Afterwards, in order to get to the final section, the Throne of the Hegemon, you must pass through an assortment of levels through white rifts. Along the way, you must fight Giratina styled people (first visit only).

Eventually, you will get to Nyx and be sent into a Inverse battle. Afterwards, Giratina will be able to be captured. Before both battles, talking to Nora will allow your team to be healed.

In the "Citadark Isle" segment of the Void Gauntlet, using Relic song will permit you to capture Moltres. In the "Cave of Origin" segment, a mysterious scroll can be obtained from a Meloetta puzzle, but this requires the ability to use Rock Climb to obtain. Hence this cannot be collected until after defeating the Elite 4 for the first time.