User blog comment:B214/Question and Answers 6/@comment-185.112.105.215-20170106035554/@comment-1359322-20170106233751

An Irregular BB is something that usually wouldn't happen but did. The CCQ and Triana which is something that normally wouldn't happen occur. Similar with Kiba and Saji. Kiba managed to merge light/holy and demonic into one. Saji managed to fuse the 4 SG together which usually wouldn't occur either.

"[That would most likely have zero possibility. To begin with, adding Sacred Gears is a dangerous action, and you can die if it goes wrong. But for this case, since you and Saji-kun are friends, and since you two understand each other, Vritra’s soul was able to revive with a miracle. But it will be hard for the same phenomenon to occur in the same way. By the way, even if a new power is added, the evil-piece sleeping inside him won’t change. The basic base is [Absorption Line] after all. The stats of his base body won’t change that much as well.]"

- Volume 7, Shemhazai explaining about Saji attaining other Vritra Gears