Finally a kunai made of paper (and a pencil)
Paper (rectangle, not square)
Pencil (new and unsharpened)
Tape (duct tape recomended)
This is pretty simple and requires little origami knowledge.
Step 1: Step one
Take a regular piece of paper and fold it in half long ways(hot dog style as the little ones would call it) and unfold so you have a nice crease. Then fold the edges in so you get a piece that looks close to the image.