Talk:MEIKO/@comment-94.248.193.101-20120830173713/@comment-5404339-20120830182239

They are counterparts - Kaito's vocal was made to match Meiko's and they are supposed to sound good together. However, their relationship is up to fans imagination. Merli and Lapis are sisters and this is the only 'canon' Vocaloid relationship.

Conclusion: they can be whatever you want them to be. Siblings, lovers, Meiko can be Kaito's grandma... You get the idea.