Torii Seal

When the Nine-Tailed Demon Fox's Yang chakra merged with Naruto, 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 the symbol of Uzushiogakure, appearing on his Nine-Tails Chakra Mode shroud. By using the seal's key, he can create several torii to imprison the Nine-Tails. Naruto then isolated the Nine-Tails' chakra in another part of him away from the beast itself in between three torii so he could access it freely. It was later revealed that the Nine-Tails isn't always bound by the torii but has freedom of movement behind its cage, but Naruto can however enter the cage freely without breaking the seal to immobilise the beast if he wants.

Influences
A is a traditional Japanese gate most commonly found at Buddhist temples and Shinto shrines, where it symbolically marks the entrance to a sacred area. Torii were traditionally made from wood or stone, but today they can be also 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 Shinto kami Inari, is very well known to hold thousands of such torii.

Trivia

 * When this seal was made, the Nine-Tails made an allusion to the Sage of the Six Paths in regards to the seal, but the beast never finished its statement.