When you are battling Alecto in her Kraken form, watch for the moment when you are first forced to strike a tentacle. A prompt to use the R1 grapple move will appear, but you can ignore it and use regular attacks on the tentacle instead. As you do, your rage meter will fill and then remain full, which makes it easy to earn the trophy that is awarded once you manage to keep your rage meter full for 2 minutes.