Space-Time Kunai

The Space-Time Kunai are special kunai utilized by Minato Namikaze and Koga Tensei to utilize their Space-Time Ninjutsu, the Flying Thunder God Technique for Minato and the Silver Flash Technique for Koga. They look like a standard kunai except they have three blades instead of one and on the handle is the "formula" for both Minato and Koga teleportation abilities. The prongs on them also makes them more deadly in melee fighting. He seemed to prefer using these special kunai over the standard kunai.

Minato gave one of these kunai to his pupil Kakashi Hatake, as a gift for his promotion to Jōnin. During the war between Konohagakure and Iwagakure, the ninja from the former threw these kunai all over the battlefield, in order for Minato to teleport all over the place to slay his enemies instantly. He also kept at least one of these blades at his home, so he can teleport there.

Trivia

 * It is implied that touching the kunai activates a Jikūkan Ninjutsu like Minato did to the Nine-Tails' attack with a Space-Time Barrier after using hand-signs.