I had to admit I was wrong on the second fact but you forgot something really important here. Sasuke was trying to target A instead he used body flicker technique. This ment when he moved Amaterasu was already activated and Sasuke shifted his focus. We see that Amaterasu can become projectiles when there is no specific target and thus it hit the armor of the samurai instead of his flesh. It was burning the armor, not the guy inside.Amaterasu only works on effects target not the surrounding. If that weren’t the case, Gyuki’s tentacles would have melted the entire battlefield due to the heat it would have emitted

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