The user leaves on another shinobi's Sharingan a seal containing Amaterasu. The bearer does not control this flame. Activation happens on its own, when his eye sees a target pre-selected by the user of the seal. At the moment of triggering, the bearer's Sharingan takes on the form of the Mangekyō Sharingan of the one who placed the seal, and Amaterasu is activated on the target.