User blog comment:B214/Volume 23 discussion blog/@comment-172.56.16.153-20170417140249/@comment-9595671-20170417141404

Yeah, though technically he didn't kill Vritra, he ripped his consciosness into shreds whihc resulted in multiple sacred gears with his power.

In DxD, a Dragon will eventually self-revive if it's soul is intact, Nidhoggr especially. This is why some like Ddraig and Albion were turned into Sacred Gears to avert this issue.