The development of the Kagamines began when Crypton formulated the concept of making a pair of female and male voicebanks. The first idea was for two voices of a girl and an identical male of the opposite gender, just like twins. Crypton originally had the intention of distributing them as twins, but this was not adopted. Crypton stated that they approved of the many different interpretations of Rin and Len's relationship that they saw in different works. Crypton's final announcement was that the Kagamines were neither siblings nor lovers. Wat described them as two bodies with one soul. When the Kagamines were being recorded in , their names were not yet decided.