Amaterasu produces black flames at the focal point of the user's vision. In most situations, this makes Amaterasu impossible to avoid. However, if the target can move fast enough to prevent being focused on, Amaterasu will miss them when it's cast. Once created, it can continue burning for seven days and seven nights. The flames cannot be extinguished with water or any other normal methods; only the user can put the flames out.
This ability counts as a 10th level jutsu (costs 30 chakra to activate) and has a ranged attack to hit. If the user hits this touch attack, the target is allowed to make a fortitude save or take the caster's character level d10 points of fire damage (a 20th level character deals 20d10 points of damage) the target will also catch on fire, taking 2d8 + 1/character level ( 2d8 + 20 at level 20) points of fire damage per round for a number of rounds equal to the caster's highest level of jutsu they can cast. Unlike normal fire damage, Amaterasu is not reduced by any effect that grants resistance to fire damage. A successful fortitude save means that the target only takes 1 point per caster level of fire damage and does not take the continuous damage effect.
Having EMS reduces this activation cost by the level of highest level of jutsu the character can cast (with 9th level jutsu Amaterasu would cost only 21 points of chakra.)