User blog comment:Crimson and Darkness/Volume 25 discussion blog/@comment-34061653-20180624161240/@comment-29963364-20180624224944

It was never really stated what the "Infinity Attribute" actually does, but we do get hints during Issei's fights against Rizevim and Apophis.

Before Issei unlocked DxD G, Rizevim would use his [Sacred Gear Canceller] ability to negate any of Issei's attacks, and deactivate the Boosted Gear by touching it. But after Issei unlocked DxD G, his attacks became immune to Rizevim's ability. It was explained that while Rizevim could cancel the powers of Sacred Gears, there was a limit to how much power he could negate. If a Sacred Gear was powerful enough, Rizevim wouldn't be able to negate all of it.

During the fight with Apophis, Issei's attacks were absorbed & dissolved by Apophis' Darkness. But after Issei activated DxD G, his attacks were able to "pierce through" the Darkness and hit Apophis.

What I think the "Infinity Attribute" does is make Issei's attacks immune to any ability that would somehow decrease, negate, nullify, absorb, etc. his power

For example, I think Issei would be immune to Vali's [Divide], [Half Dimension] or [Compression Divider] abilities.