宝石と謎とプリンセス (Houseki to Nazo to Princess)

Background
The song was first uploaded on November 14th 2011. It was Yuugou-P's first collaboration with 7:24. Along with Strawberry sung by Rin and Pink Rose sung by Len, it became one of his few most notable Kagamine works.

Later; the original illustrator 7:24 made a fanmade PV of the song, however, she listed it as a fanmade PV which "supposed" to have no relation to the original story of the song whatsoever.

It tells a story of a boy (Len); who was worried of the Princess' (Rin) happiness. She seemed somewhat down and the Princess decided to send him on a quest to find a diamond. It was a riddle, that she gave him, something that no one have solved before. Later the boy and the Princess goes along very well, and by the end of the song, the boy finally found the diamond.