Kagamine Rin & Len

Kagamine Rin & Len (Japanese: 鏡音リン・レン), sometimes referred to as Rin & Len Kagamine, are humanoid personas voiced by a singing synthesizerapplication developed by Crypton Future Media, headquartered in Sapporo, Japan. They use Yamaha Corporation's Vocaloid 2 and Vocaloid 4 singing synthesizing technology. Their voices are sampled by Asami Shimoda. They have performed at live concerts onstage as animated projections.

Their names are derived from the concept of 'left' and 'right', like on earphones. Their surnames came from the Japanese words for "mirror" (鏡 kagami) and "sound"(音 ne). Rin & Len were developed by Crypton Future Media using Yamaha's Vocaloid 2. Their voices were created by taking vocal samples from voice actress Asami Shimoda at a controlled pitch and tone. They were the second release within the "Character vocal series," which included the vocals Hatsune Miku and Megurine Luka. Rin was the first of the Kagamines to be illustrated and Len was made to match her, following Crypton's concept.

They received mixed results from producers because compared to Hatsune Miku, they were considered much harder vocals to use. Asami Shimoda noted that she often received comments from Vocaloid fans that Rin's voice echoes within their head and makes them feel dizzy, while Len's higher ranges were not favoured by those not fond of the pair entirely.

Despite being released as a masculine character, during the development of VY2, the vocals of Ryuto or Len were not classified as "masculine vocals" and were not considered capable of holding a low masculine tones because of it. As a result, he and Ryuto were not referenced in the development of VY2.