The achievement is unlocked when you defeat five human-sized or larger enemies while in reckoning mode and fateshift. Smaller enemies like brownies, sprites, or boggarts do not count towards the achievement. Make sure the purple gauge at the top left of the screen is full. You can check by pressing
and looking at your "Fate" percentage in the center of the screen--it must be 100%. Engage a group of five human-sized enemies or larger. Initiate reckoning mode by pressing
&
simultaneously. An
prompt will appear next to each enemy you defeat. Once you have defeated five or more enemies, go up to any one of them and press
. You will be given a button prompt that you can press rapidly to get a percentage increase on experience earned. The 'essences' of the defeated enemies will flow into you. Provided you have five or more of the defeated enemies' essence streams, you will unlock the achievement.
The 40 second video below occurs during The Commendation quest--the first quest in the Warsworn faction quest line. The player character goes north of Gorhart to Osgar's camp to retrieve a dagger. As he approaches the camp from the south, Red Legion Bandits attack. He waits until six join the fray and goes into reckoning mode. After defeating all six, and before the purple gauge runs out, he fateshifts the defeated enemies unlocking the achievement.
There is no need to try to get this achievement early. Later in the game, reckoning mode will be used to survive lethal assaults of large groups of enemies. The Legend of Dead Kel questline, for example, has many such opportunities. So, if you don't get this achievement deliberately, it will most likely come naturally during the course of play.