User blog comment:Crimson and Darkness/Volume 24 discussion blog/@comment-73.49.228.11-20180107181327/@comment-2601:8C:601:5692:70F4:6327:4182:E9AD-20180114053736

So, yeah the names of the six Extra Demon houses that served directly under Lucifer appears on the Japanese wiki. Altogether, they include: Lucifugus, Satanachia, Agaliarept, Fleurety, Sargatanas, and Nebiros.

These names are derived from the Grand Grimoire, where they are considered the subordinates of the triumvirate of Lucifer, Belzebúth (Beelzebub), and Astaroth (Asmodeus). Yes, as stated above, certain demons served certain members of the triumvirate, but that seemed to be considered of little real importance.

What's interesting is that in DxD the House of Naberius is said to have been subordinate to the House of Nebiros. This matches with the Grand Grimoire, where each of the six have three subordinates, with those of Nebiros being Ayperos (Ipos), Naberus (Naberius), and Glasyalabolas. The respective subordinates (following the order I presented above) fill the first eighteen spots of the Pseudomonarchia Daemonum equivalent to the Goetic demons, with Pruslas not matching any of the 72 Pillars. So, could these connections be true in the DxD Universe? And does this mean Pruslas is an Extra Demon house?

Furthermore, if I recall correctly, there is mention that Koneko's and Kuroka's dad served a member of the Naberius branch family. Perhaps the alternate forms of their names could be the branch family names, in this case the House of Naberus?

As to other Extra Demons that were suggested by the first anon above. It's always possible, particularly Dagon and Alasator. My opinion of Issei's title should he receive one is that it should be somewhat different but definitely NOT Satanachia.