This is Story related and will unlock around 2/3rds of the way through the story. Some more details are available in the spoilers below:
*** Spoiler - click to reveal ***This achievement pops after you complete Mission 8: Drg Tape. You play the role of The Dragon (Fifteen) and have to go through 4 rooms within the prison that you previously visited as Zero.
Not too much to worry about here IMO; Fifteen is OP compared to Zero since he can do a ranged slice that pretty much always kills anything you slice and he seems to be slightly faster than Zero too.