The 2channel users aimed to fool "Nico-Chu" (fans on Niconico Douga) by presenting Teto as an official Vocaloid, often in contrast to Hatsune Miku.
Her name Kasane implies "overlapping sound," and she was intentionally designed with chaotic, contradictory traits, such as being a 31-year-old chimera who appears as a 15-and-a-half-year-old girl.
Her voice was provided by Mayo Oyamano. Despite being a hoax, Teto's voicebank was developed and released, allowing her to be used in music production and contributing to her popularity.
Following the prank, she was released for the UTAU software, where she gained immense popularity, becoming the software's mascot.
Despite her origins as a fan-made character, her popularity led to her appearing in official media, including as a character in Hatsune Miku: Project DIVA and eventually receiving a commercial Synthesizer V voicebank in 2023.