In any game mode, choose Jago as your character.
Let your yellow bar under your health bar fill up all the way. Seems the best way to do this is to get beat up and use defensive moves (counters, combo breakers, blocks).
Once it's full, press Heavy Punch and Heavy Kick at the same time (RB + RT with default controls).
This will slowly regenerate Jago. Once you've healed some of the damage you've taken, achievement will pop. You should only have to do this once. If you already lost the first round (ko'd once), let yourself get beat up a bit more before initiating instinct mode so you can heal the full amount.