Rin Kagamine X Len Kagamine
'Rin,' meaning right, and 'Ren,' meaning left, along with 'Kagami,' which is mirror, and 'ne,' sound, all add up to "Right and left mirror voices." Therefore, Len and Rin have no relation except that of which you choose to believe. They can be siblings, best friends, enemies, or, yes, even lovers. Crypton in no way made any announcement of Rin and Len's relation, they left it up to YOU to decide for yourself.I believe them to be lovers.AND THE BEST VOCALOID PAIRING!