When Naruto first began serialization, one of the main draws to the series were the strategic battles and the unique ways in which chakra began to be utilized. As Naruto developed, some of this was lost in favor of larger-scale attacks which could simply wipe out entire armies, rendering most tactics not nearly as useful as they were prior. One of the main contributors to this exponential power scaling issue was the introduction of the Rasengan, a highly destructive technique that if utilized properly could carve away entire mountains. The Rasengan is responsible for the only villain Naruto ever kills. The secret to the Rasengan’s incredible power, however, is deeply rooted in these strategic elements
The Rasengan is first introduced to readers in chapter 150 where the Toad Sage Jiraiya demonstrates the technique to Naruto by sending a couple of thugs spinning through a wall. This marks the beginning of Naruto’s training to master the Rasengan technique through learning various elements of chakra control. In order to master the Rasengan, one must become adept at the fundamentals of shape transformation. Shape transformation is in essence the very structure of jutsu, and involves learning to control every aspect of one’s chakra flow, including shape, form, and potency.
Related: Naruto's Chakra Returns to Its Spiritual Roots in New Shonen Jump Manga
In Naruto chapter 519, Naruto attempts to form a Rasengan in Naruto's newly acquired Nine-Tails Chakra Mode. To his surprise, this attempt results in what looks like a miniature Tailed Beast Bomb. Killer Bee, who has been watching Naruto, comments that the Rasengan is “exactly like the Bijudama” and comes to the conclusion that the Rasengan must have been developed by watching
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