The In Btwn music is an Rare Fortnite music. In Btwn was available via the Item Shop for 200 V-Bucks and you can buy it from Fortnite Item Shop when it will listed.
Fortnite In Btwn Skin Details
Press play and do your own thing.
Fortnite In Btwn Skin PNG Images
Here is the PNG images of In Btwn below!