User blog comment:Crimson and Darkness/Shin DxD 3 discussion/@comment-29890029-20190812192108

In volume 23, Ajuka said that Issei want to unleash the full power of the 8 mutation pieces he need to have both GR and Ophis power to allow him to use DxD without putting stress on his body.

And AxA is Issei's true power who was reborn from Ophis and GR.

So, if he get GR's power, it should simply allow Issei to be able to use DxD at full power which would be at Dragon God-level. And AxA be .... well I dont know.