Left Arm Fuinjutsu

Form One
The tattoo in it's first form works as an open gate. People seem to ask how does he get the chakra out his without preforming any Kata. The answer is quite simple. His tattoo that is actually an active fuinjutsu on his arm serves as a way to funnel chakra out his left arm so he doesn't need to preform kata to excert it from his body. The fuinjusu also gives him the small ability to allow him to move his chakra around as if chakra threads were attached.

Form Two
With using a kata taught to him by the Uzumaki, the tattoo extends over his arms ad makes him and his chakra completely one in a way. Meaning controlling his chakra is as easy as breathing. This grants the chakra all his traits, such as the ability to absorb other chakra. This also activates the Uzumaki's healing ability that was taught to him by NarutoUzumaki, giving him the ability to slowly regrow limbs and heal his damage body as long as he is still alive.