Hey guys! I think I just found the song that is used for the game Six Books!

Obviously, if you listen to the background music during normal gameplay, it'll sound like a song but something will feel off about it. Reverse it and it'll sound like a bossa nova type of thing. I'm confident that this is the original source of the audio.

The song is called The Set for the Day by an artist called Foreign Sailor.

Link to the original song:

https://on.soundcloud.com/jDYPu

I think UD  used a heavily modified version of it, which is why there's additional instruments used unlike the original.