The Kuroneko is an urban legend created by Kitsune-san, real name Miyuki Kagome. This is the urban legend that attributed her the SHSL Urban Legend Creator by Hope's Peak Academy.
The legend is of a young girl in all black who wanders the streets of Tokyo asking people if they've seen her pet cat. The girl is said to be seen only between 9 pm and 3 am in the busy areas of the city. She is apparently harmless unless you say "yes", and don't have a cat with you. When that happens, she will get angry and scream liar at you. She grabs you by the throat and strangle you to death. If you say yes and you do have a cat, she says "thank you" and takes it from you.
The legend grew immensely in popularity when a popular idol claimed to spot the girl one late tour night on the streets of Tokyo.