The hottest damn twincest in the universe. Two characters from "Vocaloid 2" the vocal enhancers. They sing like angels, and they are mirrors of each other. Len loves his sister Rin, and Rin abuses Len. They're love is widely appreciated by the fans - they are favourites. Len is seen as a mega hotty, whereas Rin is seen more as a devious cutey. They are mirror images of each other, so if one of them leaned in to kiss the other, naturally they'd lean in as well.
Example of the unrequited "Kagamincest" love: If we love each other, it will be okay? - Len Kagamine, SPICE!