Baryon Mode

is a unique transformation accessible to Kurama with its jinchūriki.

Overview
In this state, Naruto's hair becomes spikier, standing up on on its ends with tufts on each side of his head appearing as fox ears. His whisker markings become thicker, with the upper ones on each side curving up below his eyes. The pigments around his eyes become black and stretch up towards his makeshift fox ears, and he takes on Kurama's red-slit eyes. The colouring of his clothes turns slightly darker orange, and he gains a chakra cape with a black swirl in the middle of his chest. Flowing from the back of his cape are four orange (red in the anime) chakra tails, with five more at the end of the cape; each tail has a black line down the centre that connects in the middle of the cape as a swirl.

In a process similar to nuclear fusion, Naruto's and Kurama's chakra are consumed as raw materials to produce a new type of energy. The increase in chakra was enough to shock both Isshiki and Sasuke, with the latter noting it being tremendous. When in use, it dramatically boosts Naruto's reflexes, speed, and power to such extremes that he even surpasses Isshiki's capabilities, allowing him to snatch the Ōtsutsuki's black rods out of the air before they are visibly enlarged, as well as dodge and effortlessly parry attacks. Kurama notes that because all chakra is connected, contact with an opponent will drain their lifespan as well.

Drawbacks
As powerful as Baryon Mode is, it is extremely dangerous if used for too long or recklessly. Doing so will gradually drain at the user's strength and very lifespan. Because of the extreme risk, the user must not make any unnecessary movements, nor act on any stray thoughts, focusing on only the most calculated of moves to keep Baryon Mode stable. Even more, over-usage of this form comes at an even greater risk at Kurama's life altogether, effectively killing it. Upon reaching the breaking point, Kurama's entire being will be destroyed, depriving Naruto of all the kitsune's chakra and capacities. However, the removal of Kurama from its jinchūriki will not endanger the latter's life.

Trivia

 * Baryons are heavy subatomic particles that are composed of three quarks. The most common examples are protons and neutrons, which are the particles that undergo fusion in the Sun.
 * Baryon Mode seems to embody the Will of Fire, with Naruto's chakra cloak incorporating the symbol and strongly resembling the monument in the Konoha Cemetery.