User blog comment:B214/Question and Answers 6/@comment-2607:FB90:603D:5340:4082:7A47:2AEA:26C5-20190115200556/@comment-207.242.44.6-20190116203017

here a quote from volume 21

"The original meaning of Balance Breaker referred to a forbidden move of the Longinus. Azazel proposed that the possibilities of a Balance Breaker could be roughly divided into three types. The majority of Balance Breakers, including subspecies, could be classified as strengthening, evolving to a point of transformation. By pursuing the arrogance of themselves and the Sacred Gear, one would fuse together with their Sacred Gear to produce the Abyss Side. This was the type that Vali and Ikuse Tobio belonged to. Finally, there were those that couldn’t be categorised by this system due to their sudden variation, and those were the exceptions among exceptions. This was Hyoudou Issei, Kiba Yuuto’s Holy-Demonic Sword, Gasper Vladi, and Saji Genshirou; something had happened in relation to the Gremory peerage. In particular, Hyoudou Issei, Gasper Vladi and Saji Genshirou had also reached the Abyss Side. It could be described as an extremely abnormal generation. The phenomenon that was originally impossible began to occur frequently around Hyoudou Issei. Azazel was also quite intrigued by this."