Kagamine Len, as I've introduced before, is a Vocaloid.
Follow the link to know more about Vocaloids, but simply put they are 'vocal synthesizers. Programs used to make 'songs' like a voice box. What makes them different is, they are very good examples of "virtual divas". As they have their own personalities and merchandise. (They also have a rhythm game)
Len Kagamine with his hair down all in black,
what's not to like?
Aside from the usual tragic theme of the twins being separated at birth and having to face each other to the death, there's the charming costumes and that seriously powerful song and it's lyrics.
"Karakuri burst" is a serious treat for anyone who likes the twins and a good start for those who want to try their music!
I specially like the character design/illustration by Suzunosuke and the song by Hitoshizuku. This particular song makes use of the 'upgraded' or strong 'append' versions of Rin and Len.
And it's seriously EPIC.
I honestly just LOVE the twist (however cliched it maybe)