This one is a gimme. Simply go to "Story" in the menus, select "Remix Heart Gaiden" and watch each of the 4 episodes. If you want to make this go faster, press Options once the text begins and change "Text Skip" to "All Text". With this, you can press R1 and select "OK" to skip through the entire chapter. Or you can watch it for a bit of backstory. Either way, once you've watched all 4 episodes the trophy is yours.