Characters in Korean Lost Saga are entitled "mercenaries". In the North American version, they are called "heroes". Mercenaries are divided into five different categories: Melee, Ranged, Magic, Special, and Premium. Players can purchase mercenaries from the in-game shop using pesos, the currency earned from battles, or earn their services for 2 hours when they reach the rank at which that mercenary is unlocked, with the exception of premium mercenaries, which can only be obtained through gold (KLS's cash currency) or through mercenary scrolls, which can be purchased for 3,000 pesos in the shop. Players may obtain as many mercenaries as their inventory slots allow. By default players are allowed 12 Mercenary Slots and more can be added by purchasing the slot item from the shop.
Once players place their mercenaries in the inventory they can switch between them by pressing number keys (this can be changed in the options menu). This method allows the players to freely change into different mercenaries during gameplay, but only if the mercenary that is currently in use has 4 gears equipped.
In addition, "epic gears" are mercenary equipment with an alternative design. They enhance the game by allowing players to equip different gears to the mercenaries they've hired. However, epic weapons can only be equipped to their corresponding mercenary. Epic gears provide not only a change of costume, but a stat boost that varies with each gear. The gear's skill, however, does not change. Premium mercenaries do not have epic gears, but they are able to equip them. There are also special gears titled "legendary gears". Unlike epic gears, these gears do not correspond to any existing mercenary. As such, legendary gears have no alternate design and there are no legendary weapons.