Kaai Yuki (歌愛ユキ) is a Japanese VOCALOID developed and distributed by AH-Software Co. Ltd., and was initially released in December 2009 for the VOCALOID2 engine. Yuki's vocals are based on an elementary school student. With her voice provider being a young girl the identity of her provider has never been revealed for legal reasons. She was the first female VOCALOID whose voice samples are not produced from an adult.
There is currently ongoing development for an upgrade to the VOCALOID4 engine, using a new voice provider for the growl components. This was due to the fact her provider had matured, making re-sampling problematic.
Yuki is meant to be portrayed as a 9 year old elementary school student. She is said to be "As tall as 10 big apples" and "As heavy as 86 apples". Her red randoseru is a motif of YAMAHA's wind controller, WX5.
The song is about Jani Schofield, who is a young girl that has been diagnosed with a very severe case of schizophrenia. She sees over 200 hallucinations and they come from her hallucinated island "Calalini". This song was made to show awareness of Jani's condition.
The original version of the song sung by Megurine Luka in English was uploaded onto YouTube on September 3, 2011. The original version got popular on YouTube and, because of demand, a full version in Japanese was later uploaded on October 31, 2011 using Kaai Yuki.
Yuki and Kiyoteru were announced in November 2009. Interestingly, at the end of the previous month Crypton Future Media had just made their own announcement of a series called Project if..., which was set in an elementary school setting.