Crow

are the trademark 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 in corporation with his genjutsu as well as ninjutsu while fighting — often time de-materialising into a flock of crows or else summoning them from underneath his cloak to blind his target.

Known Crows
The most notable crow Itachi has ever summoned, possessed his best friend Shisui Uchiha's Sharingan in its left eye socket. Itachi stored this clone 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 resurrected, he was forced to summon the crow and have it use Shsui's ultimate Mangekyō Sharingan technique on him: Kotoamatsukami in order to free himself from Kabuto Yakushi's control. Itachi seemingly not wanting the eye to fall into the wrong hands, 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.