Itachi's Crow

It was one of Itachi Uchiha's crows that had Shisui Uchiha's left eye implanted into it. It was later stored inside Naruto Uzumaki.

Background
Before his death, Shisui entrusted his remaining eye (having been robbed of his right eye by Danzō) to Itachi to protect Konohagakure. Itachi would later implant the Sharingan into this crow.

Itachi Pursuit Mission
During an encounter with Naruto prior to his final battle with Sasuke, Itachi asked Naruto what he would do if Sasuke ever attacked the village. Seemingly satisfied with Naruto's answer that he would stop Sasuke and save the village, Itachi decided to implant the crow into Naruto's body by using a genjutsu as a distraction, to allow the crow to store itself inside Naruto. Although he hoped that the time for the use of the crow would never come, Itachi arranged the crow as a countermeasure if Sasuke does attempt to attack Konoha.

Fourth Shinobi World War: Confrontation
When Itachi was reincarnated during the Fourth Shinobi World War, the crow emerged from Naruto's mouth when he indirectly activated his Mangekyō Sharingan during their forced fight. Having expected Sasuke to use his eyes to gain an Eternal Mangekyō Sharingan, Itachi arranged for the crow to respond to his eyes and implant the mental command to protect Konoha the moment he battled Naruto.

Though the use of Kotoamatsukami failed to affect its intended target, it allowed Itachi to break free from Kabuto Yakushi's control. He proceeded to reveal to Naruto the significance of his plan. But due to the ten year waiting period for Shisui's eye to be used again, Itachi incinerated the crow so that it would not fall into the wrong hands.