User blog comment:B214/Question and Answers 6/@comment-2600:387:1:804:0:0:0:58-20180529135903/@comment-28884330-20180529162232

An Abyss Side Balance Breaker is obtained through mastering and evolving the base Balance Breaker, and involves a sort of fusion between the wielder and the Sacred Gear. There is the requirement of having the “real” Balance Breaker for it, whereas a subspecies Balance Breaker can be obtained without it (it can also be vastly different from the base, whereas an Abyss Side is an evolved form of the base), and a subspecies also does not necessarily entail the fusion aspect.