Chidori

The Chidori is Kakashi Hatake's first original technique, though he more frequently uses an S-ranked version known as the Lightning Cutter. He created it around the time he was promoted to jōnin, and later taught it to Sasuke Uchiha.

Overview
This technique channels a large amount of lightning chakra to the user's hand. The amount of chakra is so great that it becomes visible. The high concentration of electricity produces a sound reminiscent of many birds chirping, hence the name. Once the technique is completed, the user charges forward and thrusts the Chidori into the target. This produces heavy amounts of damage that is usually fatal. This technique is classified as an assassination technique because of the speed at which it is performed, despite the loud noise it produces.

As shown against Killer B, Chidori can also be used to simply give the opponent a large electrical shock without impaling them.

Drawbacks
This technique has a major drawback, however. The speed at which the attack must be done, combined with the fact that the user must run in a straight line, causes a tunnel vision-like effect for the user. This allows the enemy to easily counter the attack, making it a potentially lethal move for the user. Though this drawback would seem to make learning the technique fairly pointless, Sasuke and Kakashi are able to avoid the drawback because of their Sharingan, which takes in every detail, regardless of how fast the user is moving.

As an additional drawback, the large amount of chakra required limits the number of times this technique can be performed per day. In Part I, Sasuke can only use it twice a day (under his own power) and Kakashi can use it four times, though their limits have been shown to have increased to an unspecified level in Part II. Should the user attempt to go beyond their limit, all of their chakra will be drained and their very life force could go along with it.

An additional problem, though not necessarily a debilitating one, is the fact that the large amount of chakra can also injure the user's hand if they put too much force into the attack. In Part I, Sasuke does this when confronting his brother Itachi, causing some of the skin to peel from his hand and leaving it slightly smouldering after the attack was finished.

Use and Improvement
Originally, when Kakashi invented the Chidori, he suffered the drawback of the technique being a straight-line attack, which prompted Minato Namikaze to tell him not to use it, as the risk is too dangerous, and the technique would be rendered useless as the targets could simply evade or easily counter it. However, after acquiring the Sharingan from his friend, Obito Uchiha, Kakashi has eliminated the drawback, as he can predict the opponents' movements and aim at them much easier, making it rather difficult for the enemy to evade the attack. Sometime after mastering the Chidori, Kakashi improved it into a far more powerful version, the Lightning Cutter, which he uses more often than the Chidori itself. The Lightning Cutter is powerful enough to drive a hole through the chest of a person struck by it, as seen when Haku protected Zabuza from Kakashi.

Kakashi taught Sasuke the Chidori as a means to persuade him not to use the Cursed Seal of Heaven as well as to forfeit his desires for revenge. He also emphasised that the Chidori was a blade to protect his friends. Unfortunately for Kakashi and the others, Sasuke has warped it into a blade to sever those bonds in his desire for power and vengeance. In Part II, Sasuke has mastered the principles of lightning manipulation and developed a number of other Lightning Release techniques, most of which are derived from the Chidori. Sasuke can also transmit his Chidori through weapons as he does with both his sword and with his fūma shuriken.

After attaining half of the Sage of Six Path's power, Sasuke was able to enhance his Chidori into a form capable of piercing Madara Uchiha while a jinchūriki of the Shinju.

Cursed Seal of Heaven's Influence
Sasuke has shown that by forcing more chakra from the Cursed Seal of Heaven, he can use an additional Chidori after reaching his daily limit. Despite the significant power gained from the Cursed Seal's influence this Chidori, identified as, is essentially the same technique. Rather than the bright hues and chirping noises that are normally associated with the Chidori, this particular variant emanates a dark gleam along with the distinct sound of flapping wings. Sasuke has not been seen using this form of the technique since his fight with Naruto at the Valley of the End, and it is presumed that the ability to do so was lost along with his Cursed Seal during his battle with Itachi. In the first Ultimate Ninja Storm game, it is referred to as "Chidori Lament" and in the Path of the Ninja 2 game, it is referred to as "Dark Chidori".

Rinnegan Influence
Upon gaining the Rinnegan and Hagoromo Ōtsutsuki's chakra, Sasuke was able to empower his Chidori. After doing that it becomes strong enough to not only bind Madara Uchiha in his Ten-Tails' jinchūriki form, but cut him right in half.

Trivia

 * The name Chidori comes from a story about famous samurai (22 April 1513–2 November 1585). Tachibana was in possession of a famous sword called . One day, while he was still a young man, he was taking shelter under a tree, as it was raining. Suddenly, a bolt of lightning struck him. However, Tachibana used his Chidori to cut the Thunder God inside the lightning bolt, allowing him to survive. After this incident, he renamed his Chidori to.
 * In the anime, Chidori looks like a white, sphere-shaped amount of electricity that emits small lights that surround the palm. In the manga, it has no form. It is just a coverage of electricity all over the hand. Starting from the Part II of the anime, the appearance of Sasuke's Chidori changes to resemble the one in the manga.
 * can also be translated to "plover".
 * In Naruto: Ultimate Ninja 3, if the player customises a few characters (such as Naruto), they will be able to use this technique.
 * In the Naruto Illustration Book, one image depicts Sasuke extending a Chidori from his hand to cover multiple thrown kunai.
 * Kakashi noted that the Chidori was a blade that was created to protect one's friends.