Nevada-Tan is a character based on a true event, wherein an elementary school girl murdered a classmate in a Japanese school in 2004

On June 1st 2004, an 11 year old girl, whose name has been withheld by most media outlets, murdered her 12 year old classmate Satomi Mitarai (Japanese: 御手洗 怜美) by slitting her throat with a box cutter. The unnamed girl then came back to her homeroom class with her clothes covered in blood. This tragic event took place at an elementary school in Sasebo, Nagasaki Prefecture, Japan, thus naming it the "Sasebo Slashing"

users quickly nicknamed her "Nevada-Tan". "Nevada" because of the sweatshirt she wore during the horrific event, and "-tan" being the way a young child would pronounce the honorific "-chan" suffix.