Rasengan

The Rasengan is a technique invented by the Fourth Hokage, after three years of development, though it was never completed. The Rasengan was meant to be an example of nature manipulation as the Fourth meant to combine his chakra element with the Rasengan. However, he died before he could accomplish this. Despite this, the Rasengan is still a very useful, if difficult to learn jutsu. As Jiraiya trained Naruto how to use it, learning the Rasengan was broken into three steps. The first was to burst a water balloon by spinning the water inside in multiple directions at once using only the user's chakra, which emphasizes rotation, then one has to burst a rubber ball and since rubber is thicker and air is completely different from water, it forces the user to use denser chakra to break it, this step emphasizes power, the last is to combine steps one and two by spinning chakra inside a balloon without making it move at all.
 * Name: Rasengan, 螺旋丸, literally "Spiraling Sphere", English games "Power Strike"
 * Type: A-rank, Offensive, Short range (0-5m)
 * Users: Fourth Hokage, Jiraiya, Naruto Uzumaki, Kakashi Hatake

Because the Rasengan doesn't use handsigns, it relies only on the chakra control of the user, and once it's complete, it becomes self-sustaining. The chakra spinning at such a speed and compacted into such a small state allows the spinning chakra to grind whatever it comes in contact with, causing major damage to it, and can even cause internal damage. And because the Rasengan is just pure chakra, it doesn't have a definite limit of use like its counterpart, the Chidori has.

While the Rasengan is a one-handed technique, in Part I, Naruto has to use three or more hands to use it, mostly due to his poor chakra control. He requires to use of his one hand to create the shell, and a shadow clone's hands to spin the chakra. After the timeskip, Naruto was shown to be able to execute a Rasengan easily with one hand. When he goes into his one-tailed transformation, he was able to make a Rasengan using his hand to spin and the Nine-Tailed Demon Fox's chakra shield to create the shell. Because he mixed it with the demon fox's chakra, the Rasengan had a purplish glow, making it equal in power to Sasuke's Flapping Chidori.

While in training, Naruto improved the Rasengan with the Odama Rasengan, or Great Ball Rasengan. Later Naruto mixed his Wind natured chakra to create the Wind Release: Rasengan as it was originally intended.