You are unlikely to earn this achievement unless you specifically try for it, or are not using any Essence at all for the majority of the game and killing lots with Ultimate Techniques. The best method that I have found is to head to Drawbridge Square in Chapter 16, where there are the 3 Military Ghuls. Each of these if killed with a UT is worth about 7000 Essence, without any boosts. They respawn if you leave and come back to the area, so after they are killed, use the door with one blue dot on and then go back, they will have respawned. Even from 0 Essence, 5 times doing this will get you 99999.