Vocaloid : Kagamine Twins [Story]

Just to avoid wrong assumptions about the twins, first of all, it's not twincest lol,
second of all, they are not really blood-related..
here's the proof

Their family name was chosen by combining Kagami (鏡 ,Mirror), Ne (音 ,Sound), with the first syllables of their given names a pun on "Left" and "Right". They are not actually brother and sister, but are reflections of a mirror

Source [Wikipedia]

Watch the video accordingly.
Kagamine Twins story with English subs.

Kagamine Rin - Aku no Musume [Daughter of Evil]

Kagamine Len - Aku no Meshitsukai [Servant of Evil]

Kagamine Rin, Len - Message of Regret

Kagamine Rin - Kokoro

Kagamine Len - Kokoro Kiseki

Kagamine Rin, Len - Kokoro-Kiseki [mixed]