User blog comment:B214/Volume 17 spoilers./@comment-24421137-20140221065803/@comment-24468758-20140221072900

The rankings in DxD are always connected to power. Angels and Fallen Angels can be ranked by the number of wings as everyone with ten or twelve wing is leader class and belongs to the strongest (Fallen) Angels:

12 Wings: 4 Great Seraph, some of the Fallen Angel leaders, perhaps some other Seraphim

10 Wings: Dulio (Leader of DxD, Longinus possesor), Kokabiel