We Love Katamari REROLL+ Royal Reverie - Night School - 6 Sounds (100%) [WR]
There are normally 5 Sounds (instruments) to gather up in the stage. However, there is occasionally (perhaps 5% of the time) an extra one that appears on the desk above the one in the starting room. If you look closely, you can see it from any of the 3 spawn points if you turn your katamari toward it.
Sadly, as others have observed, the game hardlocks (black screen with no response to inputs; closing the game and restarting is the only option) just after the results screen. So you can't save your game with 6 Sounds.
Thanks to @Jobnsoso for the information about the 6th instrument. Curiously, his game didn't lock up afterward.
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