Accordian Songs, also called "Notes", are a collectible item that currently only allow Reshnha to open specific locked doors, or change the appearance of some NPC's and specific items. Once collected, these songs can be played by pressing shift when no effects are equipped. There are currently only 4 collectible songs, though it seems there may be more added in future releases as Stomidori's letter states that some songs can be used to travel to different locations in the Dream World. Cerasus' Itch.io page also states that Reshnha will need to collect all songs in order to escape the Dream World.
Crimson Notes
"In this day, you died once more.
I was too late."
Unlocked By:
Unlockable Locations:
Debtor's Room, Moonbow Laundromat Back Room
Other Uses:
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Emerald Notes
"And you had nowhere to go but down."
Unlocked By:
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Azure Notes
" ██████████████████████
██████████████████████████████████
██████████████████████████████████ "
Unlocked By:
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Royal Notes
"Hello. Have you ever heard of the seventh circle of hell?"
Unlocked By:
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██████████████████████████████████
██████████████████████████████████ "