悪ノ召使 (Aku no Meshitsukai)

Background
This song was uploaded on April 28th, 2008, and has reached nearly 3,000,000 views. It is arguably Len's most notable song.

This song takes during the events of Aku no Musume, except from her (Riliane) servant's (Allen) point of view. It details the story of how the twins were separated when they were very small and how the only thing of Riliane he could ever see was her soft, kind side, and of how he killed Michaela (Miku) (after falling in love with her) and eventually traded places with Riliane to be executed. The keywords of this song are「僕が君を守るから　君はそこで笑っていて」(“I will protect you, so just be somewhere, smiling”). The official English title of the song is "His significance of existence".

This song is featured in the MikuPa Live in Tokyo Concert, the MikuPa Live in Sapporo Concert, and the MikuPa Live 2012 concert; also in the game Project Mirai (Append Version) and the EXIT TUNES compilations Vocalogemini (Append Version) and Vocalolegend. It is the second track to the Story of Evil.