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 favored by those not fond of the pair entirely. They received mixed results from producers because compared to Hatsune Miku, they were considered much harder vocals to use. Rin was the first to be illustrated and Len was made to match her, following Crypton's concept. They were the second release within the ' Character Vocal Series,' (abbreviated ' CV Series') which included Crypton Future Media's other vocaloids, Hatsune Miku and Megurine Luka. Their voices were created by taking vocal samples from voice actress Asami Shimoda at a controlled pitch and tone. Rin & Len were developed by Crypton Future Media using Yamaha's Vocaloid 2. Notice the number 02 on Rin's left shoulder in her official artwork. Their official code name, CV02, refers to their position as the second Vocaloids made by Crypton Future Media for their 'Character Vocal Series' (abbreviated 'CV Series'), succeeding Hatsune Miku (code-named CV01) and preceding Megurine Luka (code-named CV03). They have performed at live concerts together, as they are each other's mirror image. Their voices are samples of the voice actress Asami Shimoda. They use Yamaha Corporation's Vocaloid 2 and Vocaloid 4 singing synthesizing technology. Their official moe anthropomorphism consists of a pair of twin vocals, a boy and a girl, respectively named Len and Rin. Kagamine Rin & Len ( Japanese: 鏡音リン・レン), officially code-named CV02, are a pair of Vocaloid software developed by Crypton Future Media, headquartered in Sapporo, Japan.

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