If the World is an album by Yamashizuku, released at Comiket 84. It is a concept album, with each song being based on a different fairy tale. It includes nine tracks featuring various Vocaloids, but mainly Kagamine Rin and Len. A second part with more songs was released on December 20, 2014 called If the World 2.
A crossfade can be seen here.
The album can be ordered on Toranoana.