Rasengan

The Rasengan is an A-rank technique created by the Fourth Hokage, that creates spinning chakra sphere which grinds at its target and subsequently explodes. It was created by Minato Namikaze, by observing the Tailed Beast Ball. Minato spent three years developing the Rasengan; his intention was to take the shape transformation of one's chakra to the "highest possible point" and combine it with his chakra's nature affinity, creating a technique that did not need the aid of time-consuming hand seals to control. Although Minato died before he could accomplish the latter feat, this was eventually accomplished by his son, Naruto Uzumaki. Even without nature transformation, the Rasengan is still a powerful, versatile, and difficult technique to learn and master.

Usage
The Rasengan does not require any hand seals to use, relying only on the chakra control of the user. Once it is complete, it becomes self-sustaining, which does not give the Rasengan a definite limit like its counterpart, the Chidori. The compacted nature and moving speed of the chakra allows the Rasengan to grind into whatever it comes in contact with to inflict major damage. This tends to launch the target spiralling backward after being hit or, if the target is lying on or being launched to the ground, the destructive force is enough to form a crater. It has been noted that the Rasengan is superior to the Chidori by its creator, Kakashi Hatake, Minato's sensei, Jiraiya and Sasuke Uchiha after seeing the after effects of the Rasengan on a water tower. Because the Rasengan requires a high level of shape transformation, mastering the technique also grants a person mastery of shape transformation, even if the person isn't aware of its concepts. Likewise, having previous mastery over shape transformation can make it easier to learn this technique.

The Rasengan was created with the intent to be combined with the user's elemental affinities, a task too difficult for Minato to complete before his death. Kakashi, his student, tried to add his Lightning Release chakra to the Rasengan, but was unable to and explained that he used the basic idea to create the Chidori and its more advanced counterpart, the Lightning Cutter, which require a certain point of shape and nature manipulation itself. Naruto was the first to add his Wind Release affinity to his Rasengan to create the Wind Release: Rasengan, which was shortly advanced into the Wind Release: Rasenshuriken.

Learning
Despite the Rasengan's destructive potential, it can be learned using simple toys as equipment. In Part I, Jiraiya taught Naruto Uzumaki how to use the Rasengan, breaking the process into three steps:


 * The first step was learning how to burst a water balloon by spinning the water inside in multiple directions at once using only the user's chakra, which emphasises rotation. In order to complete this process, it is crucial that the user is aware of the natural rotation of their chakra.
 * The second step was for the user to burst a rubber ball. Since rubber is thicker, and air is completely different from water, it forces the user to use denser chakra to break it. This step emphasises power.
 * The third and final step was to combine steps one and two by spinning chakra inside a balloon without moving the balloon itself, emphasising stability of the sphere.

Although users generally learn how to form the Rasengan with one hand, Naruto and Konohamaru Sarutobi use one or more shadow clones to help in the creation. By having the hands of the shadow clones act as shells, Naruto and Konohamaru can complete and use the technique without using any extra time to master their chakra control.

Improvement
While Naruto had invented new ways to use a Rasengan and its variants, he still used shadow clones, and later chakra arms, to create them. By the end of the Fourth Shinobi World War, Naruto had become skilled enough to use the technique unassisted and without enhancements, with his regular Rasengan expanding to the size of a Big Ball Rasengan.

During his training with Jiraiya, Naruto improved the Rasengan with the Big Ball Rasengan. An anime exclusive flashback explained that the Big Ball Rasengan's invention resulted from Jiraiya's remark that it would be easier to hit an opponent with a larger Rasengan. Later, Naruto mixed his wind-natured chakra to start developing the Wind Release: Rasengan, as it was originally intended. Naruto took the Rasengan even further than his father by creating the Wind Release: Rasenshuriken, a variant of the Wind Release: Rasengan. While this new technique damaged the opponent's chakra circulatory system, it also inflicted the same type of damage to Naruto's arm, making it a double-edged sword.

Naruto used chakra arms in his Nine-Tails Chakra Mode in an attempt to create a new Rasengan, the Tailed Beast Rasengan, which is even more similar to the Tailed Beast Ball than the Rasengan originally was. While in this mode, he can use the basic Rasengan with just one hand. It appears that he can now do so in Sage Mode, as well.

After obtaining the power of all nine tailed beasts, Naruto was able to add Shukaku's magnet-nature chakra, as well as his sealing techniques, to the Rasengan; allowing him to create the Sage Art: Magnet Release Rasengan.

Unique to Naruto's son, Boruto Uzumaki, he was able to develop his own Rasengan variant, which can be thrown and disappear in midair.

Senjutsu Influence
Utilisation of senjutsu chakra has been shown to drastically improve the Rasengan. The most basic of these improvements being the — a simple Rasengan mixed with the user's senjutsu chakra. During his battle with Pain, Naruto was shown to have created several Rasengan variants which utilised his senjutsu chakra. Naruto also overcame the primary obstacle of his Rasenshuriken when he threw the Rasenshuriken in Sage Mode, preventing any damage done to his own body, and increasing its power, causing disintegration on contact.

Naruto can also wield a Rasengan in both of his hands while in Sage Mode. Sage Art: Big Ball Rasengan uses two Big Ball Rasengan, each the size of his own body, while Sage Technique: Spiralling Serial Spheres uses two regular Rasengan. Jiraiya is suggested to have been capable of doing something similar. When teaching Naruto the Rasengan, he held the Rasengan in one hand and demonstrated the water balloon exercise in his other hand. Both Jiraiya and Naruto can create even larger Rasengan, the Ultra-Big Ball Rasengan and Sage Art: Ultra-Big Ball Rasengan respectively. Naruto can even mass a large group of Ultra-Big Ball Rasengan and launch them at one target as the Sage Art: Many Ultra-Big Ball Spiralling Serial Spheres, which could even stun Kurama.

Nine-Tails Influence
Naruto had shown that when he was under the influence of the Nine-Tails' chakra, he could improve his use of the standard Rasengan and simultaneously make up for his shortcomings in performing the technique. The chakra shroud surrounding him in his one-tailed form served as the shell to stabilise the Rasengan's chakra, thus he did not need a clone to help as usual. Due to the influence exhibited by the Nine-Tails' chakra, this Rasengan changed from its yellow or blue colour to a purple, orange, or red colour, made stronger than its standard version. Despite the fact that some video games give it its own name,, , and , it is fundamentally the same technique.

During his training with Killer B, Naruto was informed that the Rasengan follows the same properties as the Tailed Beast Ball, in that it's a technique that compresses chakra into a ball. The main difference between the two is the rotation used to stabilise the Rasengan. Because the Tailed Beast Ball is unusable unless Naruto can completely transform into the Nine-Tails, he must instead learn how to form a Rasengan by mixing a balance of black "positive" and white "negative" chakra at an 8:2 ratio. Eventually, Kurama began cooperating with Naruto and he became able to use the Tailed Beast Ball and Super Mini-Tailed Beast Ball, leaving the Tailed Beast Rasengan unfinished. Naruto has also created new variants of the Rasengan with chakra arms while in Nine-Tails Chakra Mode such as the Spiralling Strife Spheres, the Spiralling Absorption Sphere, and the Planetary Rasengan. Using the chakra arms, he is also able to create a miniature version of the Rasenshuriken with just his index finger and two small chakra arms.

During the battle with Obito Uchiha, who had become the Ten-Tails' jinchūriki, the reincarnated Minato was able to assume the form of the Nine-Tails, due to having its Yin half sealed within him. He was then able to use the Nine-Tails replica to produce a giant Rasengan, proportionate in size to the replica itself.

When Naruto's Rasengan, enhanced with Yin Kurama's remaining chakra, clashed with Sasuke's Blaze Release: Kagutsuchi-enhanced Chidori, the impact was able to completely destroy Hashirama's and Madara's statues at the Valley of the End with the sheer force of both attacks also costing Sasuke his left arm and Naruto his right.

Trivia

 * The colour of Naruto's Rasengan has been both consistent and inconsistent throughout the series. In the manga and associated materials, the Rasengan was yellow while in the anime and its associated materials it has been blue. However in supplement materials, such as films and art books, the Rasengan has been orange, blue, or red.
 * In the second Naruto: Shippūden movie, Naruto performed a Rasengan on Shinnō without the aid of shadow clones.
 * In the anime, Naruto was able to throw his Rasengan, though he is not shown to be able to throw it in the manga.
 * In Naruto SD: Rock Lee no Seishun Full-Power Ninden, Naruto has been shown creating Rasengan with either his one hand or both of his hands and has also been shown to throw his Rasengan.
 * Minato tried to combine either Fire, Wind or Lightning Release to his Rasengan, but the task was too difficult to complete before his untimely death. Likewise, his disciple Kakashi attempted to do so with Lightning, but also failed due to the difficulty.
 * In Naruto: Ultimate Ninja 3, Jiraiya can spew Fire Release onto his Rasengan, creating the Fire Release: Great Flame Rasengan.