Crow

are the characteristic summon of Itachi Uchiha. At some point in time, Itachi made a contract with crows which allows him to summon them as he wishes. He mainly used them combined with his genjutsu as well as ninjutsu while fighting — often de-materialising into a flock of crows or summoning them from underneath his cloak to blind his target. He also used a variation of the Clone Technique called the Crow Clone Technique where he used his crows as a medium to create a copy of himself which, when hit, dispersed back into crows.

Known Crows
The only distinguished crow Itachi has ever summoned possessed his best friend Shisui Uchiha's Sharingan in its left eye socket. Itachi stored this crow within Naruto Uzumaki right before going off to fight his brother Sasuke and hoped that for Naruto's sake, he would never have to use it. Some time later, during the Fourth Shinobi World War, when Itachi was reincarnated, he was forced to summon the crow and have it use Shisui's ultimate Mangekyō Sharingan technique on him: Kotoamatsukami — in order to free himself from Kabuto Yakushi's control. Seemingly not wanting the eye to fall into the wrong hands, Itachi later incinerated the crow with the flames of Amaterasu, stating that Shisui's eye would be of no use to them for at least another decade.

An anime-original crow usually appears in the background as a comic relief, making the crow that sounds like whenever Team Kakashi makes a blunder, adding insult to injury.

Other Uses

 * Aoba Yamashiro's Scattering Thousand Crows Technique makes use of this animal as well. Whether or not these are summoned creatures is unknown.

Trivia

 * There is at least one crow mentioned in Shintō. Amaterasu, the goddess of the sun, had a three-legged crow named Yatagarasu. Interestingly enough, in addition to using crows in his techniques, Itachi has a technique named Amaterasu. He used this attack against Nagato's Giant Drill-Beaked Bird, which also had three legs.