Hate Reset or Enmity Reset refers to an additional effect of certain moves or abilities used by (primarily high level, or mission BCNM) enemies which resets the game's internal tallies of which party members have accumulated hate to their minimal levels (see Enmity). In most cases, only the targeted party member with the highest enmity (even if multiple party members were hit by the attack) will be the one to have his or her hate reset, although some moves may reset hate for multiple party members. Hate reset is not necessarily the same thing as losing aggro; players struck by a hate reset attack will still be on the mob's hate list and that player will still be attacked if there are no other players on the list.
The primary danger of this move is when its distance is not extensive. Parties may find that their Tank and front-line Damage Dealers have lost all the hate they have accumulated, but the back line support jobs and mages have not. This may cause the mob being fought to suddenly rush the mages, who (especially when unprepared for such an event) may be far less equipped to handle the attacks they may suffer than the tank.
It is very important for parties to be aware of a mob's use of a hate reset attack or ability, and the actual area in which it will affect members of the party. For instance, Kam'lanaut's hate reset move in Return to Delkfutt's Tower is an area of effect, but the radius is not very wide. It is very common for him to rush the back line mages after using this move, and all members of the party need to be ready to get hate back under control and in the hands of the tank. Tonberries on the other hand, have a single-target move, Throat Stab, which will only reset the hate of the target of the attack. These hate reset moves can be somewhat easier to deal with, as the damage dealers of the party will likely have accumulated enough of their own hate to hold the mob away from the mages until such time as the tank is able to recover.
Another important factor is that attacks that cause hate reset tend to have a few seconds delay after the attack occurs before the hate reset occurs. Tanks should generally avoid immediately trying to perform hate-building actions right as a hate reset attack occurs, because these actions might actually have their hate negated a few seconds later than they would expect.