Akai Rasengan

Akai Rasengan (赤い螺旋丸, Demon Fox Spiralling Sphere), also called Vermilion Rasengan (朱色螺旋丸) in other games, is the standard special move of Kyūbi Naruto in Super Smash Flash 2.

Under the influence of the Nine-Tails' chakra, Naruto can improve his use of the standard Rasengan and simultaneously make up for his shortcomings in performing the technique. The chakra shroud surrounding him serves as a shell to stabilise the Rasengan's chakra. 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.

Naruto enters his Three-Tailed Form, creates an equally powerful shadow clone to charge a specially powerful Rasengan, that later launches in front of his opponent. Unlike the normal Rasengan, that pushes the opponent onward.

Kyūbi Rasengan
Kyūbi Rasengan (九尾螺旋丸 Nine-Tailed Spiraling Sphere) is the fully charged version of the technique. This technique can trap opponents inside its radius before blowing them away with incredible knockback, much like the Ōdama Rasengan, only red, far more powerful, and capable of OHKOing opponents.

Origin
Used only against Sasuke Uchiha in the "Valley of the End", this move was powerful enough to counter Sasuke's Habataku Chidori (羽撃く千鳥, Flapping One Thousand Birds). The two techniques clashed and created an hyper-dense chakra sphere that later exploded and destroyed half the valley in the process.

Trivia

 * In the Anime and Manga, Kyūbi Naruto is able to perform the Rasengan in his One-Tailed form, so he doesn't need to transform into his Three-Tailed form to use it. In addition, he can use the technique without using Shadow Clones.