User blog comment:B214/DxD Zero: Sirzechs story/@comment-2603:3020:B0F:6700:75F0:1375:A662:BF4F-20180906144955/@comment-162.252.126.39-20180907214403

also pretty sure the 6 houses of lucifer mentioned are the extra demon houses, menationed in vol 24 Lucifuge, Satanachia, Agaliarept, Fleurety, Sargatanas, and Nebiros.