Each Chapter has an assigned song chosen after it is written. Though they are optional to listen to and will not sing up with story beats.
Family Trees :
Start Menu, Undertale OSTFirst Time For Everything :
His Theme, cover by SuriOokami on YoutubeTwo Voices :
Unnecessary Tension, Undertale OST
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The Heist
RandomThree teenagers manage to steal the crown prince's crown, but find themself in peril when caught. Through a legal loophole, they now have a week to figure how to escape from the palace before being sent to Pandora's Vault for the rest of their lives.