Senpai Slayer Kuku (SS KUKU) is a yandere, who hunts down people called "senpais", she gets a note and hunts that senpai down with he information given on the note, may a picture of that person will be on that note. And this will only happen on Valentine's day. 
Kuku was made into a urban legend. She has her own shrine that people put the notes in, "since there is love, there is jealousy."
Kuku will attack her target out of nowhere, only dealing non-fatal wounds. 