Board Thread:Naruto Discussions/@comment-25442710-20140926150531/@comment-945885-20140929035039

Personally, I've always taken it as a manifestation of Asura's Yang powers. Mostly because it takes the form of an asura, with three faces and six arms. It's also pretty small -- too small to be Kurama before being split in two, and too small to be the united chakra for all the Tailed Beasts (it was also pretty much outright stated that Naruto is the first person to have reunited their seperate chakras as Jinchuriki).

I think Naruto's Tailed Beast Mode resembles it because he has Asura's chakra and is inherited that Yang power.