Itachi's Crow

Shisui wanted to use his Mangekyō Sharingan's Kotoamatsukami to stop the Uchiha clan from carrying out their planned coup d'état against Konohagakure. Before he could do so, his right Mangekyō was taken by Danzō Shimura. Fearful that Danzō would also take his left eye and use it for ill purposes, Shisui removed his remaining eye and entrusted it to his best friend, Itachi Uchiha, asking that Itachi use it to protect Konoha. The eye was implanted within a crow for safe-keeping. In Itachi Shinden: Book of Dark Night, Shisui called on a passing crow immediately after he removed his eye. He merged his eye with the crow's, which the crow did not resist. Once the procedure was finished, the crow nodded and flew off into the night. From that point onwards, the crow followed Itachi from high overhead, such as when he left Konoha after the Uchiha Clan Downfall.