User blog comment:B214/Talk About What You Want! 3/@comment-24098614-20141127075211/@comment-24502975-20141127153920

Otaku, do you actually read the LNs, or do you just skim them, pretend you read them, and then ask nonsensical questions?

It was clearly stated by Azazel near the beginning of volume 14 that Vritra is considered an Evil Dragon but is not actually 'evil' like the others (CC excluded). It's probably just because of his power (and he may have rampaged similar to Ddraig and Albion in the past).