In Episode 6, Rotten Core, roughly midway through the level you will gain the Camo Sensen ability.
At one point in the level, the game will throw at you 2 Reconversion Leapers tethered by an Elite Enforcer. Defeat these enemies and 5 more Leapers and another Elite Enforcer will appear. As soon as they do, the game will then give you the Camo ability and a Focus block to activate it. Once activated, you have 30 seconds to make your way behind the Elite Enforcer and hit the B button to take him out.
You will encounter several of these Elites making your way through the rest of the level. If you need to build Focus, set one of your Combos (the 4-hit is pretty decent) up with all Regen Pressens with a Chain Pressen ending the Combo. This will amplify the regeneration and you will regain health lost while hitting enemies with Reconversion Shields. DO NOT hit the Enforcers, though, and lure their Leapers away from them just to be safe.
Defeat four more by using Camo, running behind an Elite Enforcer and hitting B.