Itachi's Crow

The crow of Itachi Uchiha that has Shisui Uchiha's implanted left eye.

Background
Before his death, Shisui entrusted his remaining eye to Itachi to protect Konoha. Itachi implanted the Sharingan into this crow. He stored the crow inside Naruto Uzumaki, and rigged it so that it would show itself in response to Itachi's Mangekyō Sharingan. Itachi made it so that the genjutsu would give the order "protect Konoha" to whomever was affected by it. Itachi intended this to be used on Sasuke Uchiha, as he anticipated that Sasuke would transplant his eyes with Itachi's to aid in destroying Konoha.

Shinobi World War Arc
When Itachi was revived during the Fourth Shinobi World War, the crow emerged from Naruto during his fight with Itachi and the also revived Nagato and overwrote Kabuto Yakushi's control over Itachi.