What is the power Itachi gave Naruto?

It was Kotoamatsukami, Shisui Uchiha's ultimate genjutsu, set to activate when Itachi's Mangekyo Sharingan was used on Naruto. Knowing that Sasuke would probably implant his eyes into his own, Itachi left one of his crows containing Shisui's eye (the other one was stolen by Danzo), as a means to "protect Konoha". However, this genjutsu was later used on Itachi himself when he attacked Naruto under Kabuto's control, thus freeing him.