Torii Seal

When Naruto first obtained Nine-Tails Chakra Mode, his previous seal's outward appearance had changed into a shape of one of the Sage of the Six Paths' magatama beads, along with a swirl design that resembled Uzushiogakure's symbol.

By using the seal's key, he can create several massive interlocking torii that can even immobilise and imprison Kurama with ease. Naruto then isolated Kurama's chakra in another part of him away from the beast itself in between four torii, so he could access it freely. It was later revealed that Kurama isn't always bound by the torii and has freedom of movement behind its cage, but Naruto can enter the cage without breaking the seal and still manipulate the torii to immobilise the beast if he wants. The seal's outward appearance changes slightly when Naruto forms a hand seal.

Trivia

 * A is a traditional Japanese gate most commonly found at Buddhist temples and Shintō shrines, where it symbolically marks the entrance to a sacred area. Torii were traditionally made from wood or stone, but today they can also be made of reinforced concrete, copper, stainless steel, or other materials. They are usually either unpainted or painted vermilion with a black upper lintel. Located in Kyoto, Fushimi Inari-taisha, which is the head shrine of the Shintō kami Inari, is very well known to hold thousands of such torii.
 * When this seal was made, Kurama made an allusion to the Sage of the Six Paths, but never finished its statement.