Ninja knives were used at first as gardening tools but now fantasized to be throwing and stabbing weapons, especially in popular japanese animes and mangas such as Naruto. Now you can make them yourself out of paper!
Create two square pieces of paper, preferably black construction paper. You might want to use two because it's thicker, but you can use one if you want. (Fold one corner like a triangle and cut off or fold in (folding is recommended because it makes it heavier and it doesn't waste paper)
Fold one corner to the opposite side. It should now look like a triangle
Fold a crease half way through the paper. It should now look like a smaller triangle.
Unfold the paper. Now, it's a triangle with a crease.
Take one of the short sides of the triangle (not the long one) and fold the edge to the middle.
Tucking in flap
Keep folding repeatedly until you can't fold it anymore and tuck the extra paper inside the kunai.
Squish the paper from top to bottom so that it creates a kunai shape. (Grasp by edges and press) This step isn't that necessary. It just makes a flater kunai.
Take a second piece of paper and roll it the long way and tape it.
Insert the tube into the hole.
Grab the tube and make sure you have enough so that you can hold it. The extra should be flattened.
Use a series of folds and reverse folds on the flat side of the tube to create a circle.
Tape the circle so that it stays.
Tape or staple the tube into the back of the kunai (where the hole is.)
13. take something heavy and put it inside the knife so that it can fly better. Pennies are good and cheap. This step is optional
Seal the kunai with paper or thick tape so that the heavy object doesn't come flying out when you throw it.