The Title Screen. A piece guaranteed to give you the chills.
The ☆24EFFECTS☆ remix of the theme is really beautiful and adds in various sound effects from the game in interesting ways while adding an intro. Listen.
The background music of the MOTHER segment, which is about as close to a Bootstrapped Theme as this series can get. It's also one of the few genuinely uplifting pieces in the game, and the only one that lasts longer than a few seconds. It even fades out and restarts when it ends.
The Witch Event theme was very uplifting, because here Madotsuki gets a flying dream. A break from all of the weird stuff in her mind.
Kalimba. A very catchy and psychedelic song that plays when the TV is changed to a certain channel.