Riddle Solver Series

The Riddle Solver Series is a Series by Kagamine Rin / Len. There are currently two songs, both by 姉を見事に使いこなす妹 さん

The Riddle Solver who can't solve riddles ( Kagamine Len )
The first song in the series. This tells about the two "mysteries" that the detective must solve, asking Kagamine Rin, the other detective, what happened as the mytesry "happened before her eyes".

The Riddle Solver who won't solve riddles ( Kagamine Rin )
This is the second (and currently final) song in the series. This tells the other side of the story, which Rin describes. It also mentions the murder in the beginning, and how Kagamine Len is playing the part of detective.