Eight Gates

The Eight Gates are eight specific tenketsu on a person's Chakra Pathway System. They limit the overall flow of chakra within a person's body. The basis for the idea of the chakra gates comes from the body's limits on the functions within it. This makes the body much weaker, but it keeps the body from expiring too soon. By undergoing intense training, one can learn how to open these gates allowing the user to surpass their own physical limits at the cost of extreme damage to their own body.

Usage
At age 17, Rock Lee has demonstrated the ability to open the first six gates, and by the time of Naruto and Hinata's wedding in the anime, he showed the ability to open the seventh gate. Rock Lee's son, Metal Lee, has been shown to open the gates up to the third gate, though only under Nue's influence. Might Guy, who taught Lee the skill, is able to open all eight. Kakashi Hatake can open at least one gate, as shown during his one-handed rock climbing where a shot of his brain shows the relevant point activating, as well as in his usage of the Front Lotus in the anime. Opening the gates is a difficult feat even for the most talented ninja, as Kakashi, a talented ninja himself, was surprised to find out that at that time, a 13-year old Lee could open as many as five of them.

Due to the immense amount of chakra flooding the body all at once, drastic changes can occur upon the user's body. The most common of these changes are the changes to skin colour, eruption of veins around the temples, and the eyes turning completely white. The green aura surrounding the user could be easily mistaken as chakra as in Kisame's case when fighting Guy. Guy corrected this misconception explaining that the green substance surrounding him is his sweat evaporating at a rapid rate, due to the intense rise in body temperature of the user.

The state of having all Eight Gates open is known as Eight Gates Released Formation. Any shinobi who activates this state temporarily gains power a hundred times greater than their normal level, but will die because of the damage done to their body.

Gates

 * 1) The, located in the brain, removes the restraints of the brain on the muscles so 100% of the user's strength can be used whereas normally, a person can only use 20% of their muscles' strength to keep them from disintegrating. Unlocking this gate allows the user to use the Front Lotus.
 * 2) The, located in the brain, forcibly increases the user's physical strength and temporarily re-energises the body.
 * 3) The, located on the spinal cord, allows the user to use the Reverse Lotus. The increased blood flow turns the skin red.
 * 4) The, located on the spinal cord, increases the user's speed and power. May cause muscle tissue to tear on use.
 * 5) The, located in the abdomen, further increases the user's speed and power.
 * 6) The, located in the stomach, increases the user's speed and power. Opening of this gate releases such enormous amounts of energy that it can cause nearby water bodies to form a vortex around the user. Once opened, capable users can perform the Morning Peacock.
 * 7) The, located below the stomach, further increases the user's speed and power. Only after this gate is activated can a capable user perform the Daytime Tiger. Those who open this gate will secrete glowing green — blue in the anime — sweat from every inch of their body which immediately evaporates from their own heat energy, creating an aura which people mistake as a chakra coating. Unfortunately, the side effects of opening the gate are that the user's muscle fibres are ripped to shreds, causing intense pain if anything or anyone touches them.
 * 8) The, located at the heart, requires the user to stab their chest with their thumb to direct the chakra to the tenketsu. Once opened, the user will enter what's known as the Eight Gates Released Formation. Opening this gate will cause the user's blood to emanate a flaming aura of red steam, the so-called  from all pores of their body, hair, and eyebrows. Releasing this gate uses up all of the body's energy while making the heart pump at maximum power. Exceeding the power of every other gate, the user is temporarily granted approximately a hundred times their normal power, far beyond that of the five Kage. Once activated, those who are capable can perform the Evening Elephant and the Night Guy. The side effect of opening this gate is that it comes at the expense of the user's life, causing the user to crumble to ash after their chakra runs out, having virtually cooked themselves from the inside-out. This is unlike opening the other gates, which simply injure or damage the body.

Trivia

 * In Naruto Shippūden the Movie: Bonds, Shinnō managed to use a technique that allowed him to open all eight gates without any drawbacks and survive.
 * In Naruto: Ultimate Ninja 2 and Naruto: Ultimate Ninja 3, Neji Hyūga uses a technique called Last Resort: Eight Gates Crumbling Attack to specifically block access to the Eight Gates.
 * In Naruto Shippūden: Ultimate Ninja Storm 2, when Might Guy activates his sixth gate, he mistakenly says "Eighth Gate of Joy!", instead of "Sixth Gate of Joy!"
 * In several video games, Rock Lee can unlock the seventh gate, despite the fact that in the actual storyline, he was only shown capable of unlocking the first six gates. In Rock Lee's Springtime of Youth Full Power Ninja Chronicles, he is also shown to be able to unlock an incomplete seventh gate.
 * Might Guy is the only known shinobi in history to survive activating all Eight Gates.
 * This feat, however, was only possible with assistance from an outside source. Also, Might Guy still suffered a debilitating blow to his leg as a result of using Night Guy, preventing him from resuming his duties as a shinobi.
 * Metal Lee was capable of performing this technique while under the influence of Nue.