Sharingan Lore

11. Itachi Didn't Give Sasuke Amaterasu

There is a common misconception that the reason that Sasuke wields Amaterasu like his older brother is because Itachi passed that ability down to him with the forehead tap during Sasuke and Itachi's battle.

Itachi never gave Sasuke Amaterasu, nor is it possible to permanently "grant" anyone a Mangekyou ability, unless you give them an actual Sharingan eye. Amaterasu is Sasuke's unique Mangekyou ability that he awakened when he awakened his own Mangekyou Sharingan.

By touching Sasuke with the forehead tap, Itachi transferred some of his power into Sasuke, basically a one-time-use jutsu that was programmed to activate if Sasuke saw Tobi's Sharingan. But the one-time use was only good for – you guessed it – one time. Otherwise it would have been more prudent for Itachi to have it set to repeat-kill Tobi over and over again, but that wasn't within Itachi's power, just a single jutsu attack that he sealed within Sasuke so that it could trigger when Sasuke made contact with Tobi's Sharingan.

But Itachi never gave Sasuke the Amaterasu. You cannot transfer Mangekyou abilities like that, otherwise the Uchiha would do it all the time and it would make the Uchiha clan insanely OP (even more OP than they already are). If they actually had that ability, Sasuke could've given Naruto and Sakura Amaterasu already if it were that simple, or at least given Sarada Amaterasu if it's only compatible with fellow Sharingan users (though Obito's and Kakahsi's Susano'o already proves this isn't the case).

Sasuke has the Amaterasu because he awakened his own Mangekyou and it is his own Mangekyou Sharingan ability, not Itachi's. That is why Sasuke has flame control – an ability that Itachi doesn't have - as well. Otherwise why would Sasuke have flame control but no Amaterasu flames? Itachi couldn't give Sasuke Flame Control because Itachi doesn't have Flame Control. Flame Control is an ability that is unique to Sasuke's Mangkeyou. Otherwise, Sasuke awakening Flame Control without having Amaterasu doesn't make any sense.

The reason that Itachi and Sasuke have similar Mangekyou Sharingan abilities is probably not coincidence at all, but likely indicates the Mangekyou abilities are inherited. Itachi and Sasuke are brothers, which is probably why they both have Amaterasu. It's likely that Fugaku may have had Amaterasu as well. Otherwise, Tobirama seemed familiar with the black flames (but not Sasuke's flame control), so it's possible that Amaterasu may have simply been a common Mangekyou ability among the Uchiha, but that the flame control that Sasuke has is rare.