In the latest developer post on the Final Fantasy Lodestone with specific regard to upcoming battle changes, players are told that enmity calculation will be greatly overhauled and a new UI indicator will allow them to gauge the levels of hostility they have generated. According to the dev post, mastery of enmity is critical to success in battle.
Actions that generate enmity can be divided into two main categories: direct and indirect. The former refers to actions that inflict damage or enfeebling status effects upon a foe, while the latter encompasses those that heal or fortify an ally. Different actions will increase enmity to varying extents, with the strength of the delivery (such as damage dealt or HP restored) also playing a part in the calculation. Enmity will be reset for players who are KO’d or otherwise incapacitated from battle for a certain period of time.
Read more about the system reform on the Final Fantasy XIV Lodestone.