Nee-chan

Nee-chan is a Proxy of The Slender Man from the Slenderblog Don't Shoot The Messenger. She is a very tiny girl of about nineteen to twenty years old, though she looks younger due to her height and demeanor. She is almost never seen outside of cosplay, which usually consists of a Japanese schoolgirl outfit, a short skirt with longsocks, her hair dyed pink and pulled into shortish twintails. She is a Hunter, a term used to denote Proxies that hunt down Runners, and briefly became a member of the division of Proxies that The Messenger worked for.

Nee-chan is very quick and agile, and an expert with knives of all sorts. She considers "Slendy-kun" to be her best friend in the world and is constantly perky and cheerful, though if angered (usually by someone insulting Slender Man in front of her), she flies into a psychotic, murderous rage. She has trouble distinguishing reality from fantasy and understanding that her actions have serious repercussions. However, despite her naivety and disconnect with reality, she is not stupid. In fact, she's actually quite clever and good at thinking on her feet.

Trivia

 * Nee-chan was inspired by Dokuro-chan from Bludgeoning Angel Dokuro-chan and Yuno Gasai from Future Diary, two of the most well know examples of anime yanderes.