Clear 25 songs on Muzukashii (Hard)
This trophy is obtained by clearing (obtaining a crown) on 25 different songs in Performance Mode (far left on the main menu) on the hard difficulty (represented by a tree).
Use the up and down arrows on song selection to change difficulty to Muzukashii (represented by a tree) and then clear 25 different songs on this difficulty.
Credit to HighflyerVII