I know what a yandere is, but I think you don't know it exists 2 kinds of yandere:

- the sweet yandere hiding her true personality behind a kind, innocent and shy personality => not dangerous as long as any other girl flirts with her love (ex: Rena Ryugu, Kotonoha Katsura, Miia, Misa Amane);

- the cold blooded and remorseless yandere able to commit a massacre laughing like a psychopath (ex: Shion Sonozaki, Ayano Aishi) or/and kidnap her love to keep him/her for herself (ex: Yuno Gasaï) => extremely dangerous, that's why I put Widow is this category.