Originally Posted by
Uchiha Barles
I'll speculate here on why Naruto has the same form when he draws on kyuubi chakra now that he had when he summoned the fox's power while in sage mode. During that chakra tug of war, Naruto was infused with nature energy, so it's conceivable that the kyubi chakra that Naruto extracted during the tug of war mixed with the nature energy within him, and the seal locked away that mixture of chakra instead of just the fox's. If this is true, I'd bet there's a limit to how many times, or how much demon chakra Naruto can draw upon and still take on that form, because I don't think he had as much natural energy in him as the demon had chakra to tug away.