Aftermath is a beneficial status effect in Final Fantasy XI that can only be gained by the wielders of some of the most powerful weapons in existence: Relic Weapons, Mythic Weapons, and Empyrean Weapons. Each of these powerful weapons gives its wielder the ability to use a special weapon skill; it is using these weaponskills that triggers the Aftermath effect. If the weapon has been upgraded to its ultimate extent, it will also bestow the Afterglow status on nearby party members.
Aftermath comes in three different levels. Which level of Aftermath the weapon wielder gains is dependent on how many Tactical Points they had when they used the weapon skill that triggered it; 100-199 TP is a level 1 Aftermath, 200-299 TP is a level 2 Aftermath, and 300 TP is a level 3 Aftermath. Higher level Aftermaths will overwrite lower level ones.
The exact effects of Aftermath are dependent on what weapon it has been bestowed by. Common effects include gaining a chance to attack twice in one attack round, similar to Double Attack, or having a chance to have damage doubled.