Step 1: Complete the game / Catch all Fish / Locate all Chests / Find All Collectibles
To begin, you’ll want to play through the game on easy or normal whilst following this walkthrough. This will help you find all Fish, Dishes, Cards, Books, Character Notes and Quartz the game has to offer. Along with this you’ll find all Chests, fill out the Batte Book, and complete all Side/Branch Campus Quests which unlock a fair amount of the Trophies.
Step 2: Replay the game on Nightmare / Unlock the remaining Bonding Trophies
Once you’ve finished the game you’ll want to carry all your stuff over to a second playthrough on Nightmare. During this playthrough you’ll be able to unlock everyones Bonding Trophies due to having unlimited bonding points and finish off any unfinished battle related trophies.
Upon completing the game you’ll be a proud owner of the Platinum Trophy.