Kaai Yuki is a VOCALOID2 sound source and character developed by AH-Software, released on December 4, 2009. She is characterized by a distinctive whispering voice mixed with mechanical sounds, creating a uniquely dark and atmospheric quality. Her vocal range spans F2 to C4, with optimal performance at tempos between 50-150 BPM. The character is depicted as an elementary school student and has become known for songs with cynical and dark atmospheres. Since 2020, her voice has gained popularity among new producers, particularly for creating high-quality songs with gloomy or melancholic themes. Her illustrator is Ataro Umetani, and her original voice provider remains unrevealed for legal reasons.