Naruto: Why Is the Rasenshuriken a Forbidden Technique?

The Naruto series has its fair share of inexplicable abilities and overpowered techniques, yet only a few in particular have been deemed forbidden. The shinobi world has strict criteria set in place to categorize jutsu as forbidden techniques, yet it’s odd to witness a few fairly common jutsu to be classified as forbidden. Naruto’s signature Rasenshuriken is one such technique that bears the mark of being a Kinjutsu (a term used for forbidden techniques).