Spiralling Serial Spheres

The Twin Rasengan technique is simply the simultaneous use of two Rasengan by the user, with one in each hand.

Trivia

 * Though unnamed in the manga and anime, this technique was named in Naruto the Movie 2: Legend of the Stone of Gelel.
 * When Naruto performed this technique in the movie, he used two different versions of the Rasengan, the Gelel Rasengan, with the aid of Temujin (who helped form it like a shadow clone would normally), and the Demon Fox Rasengan, with the aid of his shadow clone.
 * Jiraiya does something similar when teaching Naruto how to use the Rasengan; in one hand he forms a regular Rasengan, and in the other he does the balloon exercise.