Kagamine Rin is a female Vocaloid software voicebank developed by Crypton Future Media in Sapporo, Japan. She was released in 2007 as part of the VOCALOID2 Kagamine Rin & Len software package along with her male counterpart, Kagamine Len. The two characters are based on the concept of twins, with Rin's name referring to the "right" audio channel and Len's name referring to the "left". Their surname, KAGAMINE, means "mirrored sound". The voices for Rin and Len were recorded by the same Japanese female voice actress, Asami Shimoda, who sang within her chest for Len's voice. Although Crypton originally intended to distribute Rin and Len as twins, they later stated that the characters are neither siblings nor lovers. Instead, they have approved of the many different interpretations of their relationship that have appeared in various works. For example, during the production of their Append, Wataru Sasaki, also known as Wat, described them as "two bodies with one soul".

Kasane Teto is a Japanese UTAU who was originally created as a troll "VOCALOID" by fans.She is an UTAUloid and a Vipperloid. She was released by a group called the Vippers as an April Fools joke meant to fool people that she was Crypton Future Media's new Vocaloid.Kasane Teto is a chimera, she isn't male or female, but uses she/her pronouns. She is 31 in chimera years, but 15.5 in human years. Her outfit is similar to Hatsune Miku's but pink and black themed, and she doesn't wear a tie, her top is buttoned together. She has two pink twin drills, and pink eyes as well.Since Teto is a chimera, her age is technically 31, but her human age would be 15, 15 and a half, to be exact.Her hair is red, but in some depictions her hair has orange!