Kentaro's rival, Shinji Sasaki, has the appearance of a human, but that's only a disguise. In his true form, he's a Swallow furry, and in this form, his speed excels greatly.

Shinji also wields the weapon of his ancestor Kojiro: the naginata. However, he rarely uses it, except to use Kojiro's signature technique, the Swallow Reversal. Despite this, he has proven to be a great master of the sword.

He's kept up his human disguise for years in his village, but now that he's chosen to abandon it in order to train, he's chosen to embrace his inner swallow, and finds this form suitable for his protection, since his fellow ninja aren't familiar with his furry form.

Theme/"Hayabusa"
http://www.youtube.com/watch?v=wpgZ0xsEJZ8