User blog comment:Piyush Banerjee/Shin DxD 2 discussion/@comment-37165251-20181202115344/@comment-28884330-20181204063619

"Vali had a grand aim, he wanted to become stronger than anyone else, he wanted to become the [True White Dragon God Emperor]. Stronger than the sofu who abused him, his chichi, and anyone else. He would develop the ability that he was born with to the utmost limits."

From Volume 21. And it's also in his page, though it is not cited for some reason.