Enhance Your Weapon
What to kill and where to find the goals.
Repeatable: the items to hand in drop from the targets without limits, and you can run it again and again. Go kill those mobs and the quest comes along for free.
This is an exchange chain: the reward is collected as items traded at an NPC — the shop's full stock is not laid out here.
Quest steps

Many Magisters and Maestros have been recruiting volunteers to form a united front against the coming dark days. They have developed methods of strengthening weaponry as a way of empowering individual members of their forces. They tell you that now is the time to grow individual strength to prepare for the approaching darkness and ask you to learn to use enhanced weaponry... Monsters that Soul Crystals can be used on - Antharas' Lair: Malruk Knight, Malruk Berserker, Malruk Lord, Limal Karinness, Karik, Pytan, Pytan Knight Devil's Isle: Bloody Bat, Unpleasant Humming, Death Flyer, Fiend Archer, Musveren, Zaken's Royal Guard, Kaim Vanul, Pirate Zombie Captain, Doll Blader, Vale Master, Sairon, Sairon's Doll, Sairon's Puppet, Light Bringer Timak Outpost: Timak Orc Series, Timak Orc Troop Series Fields of Massacre: Doom Servant, Doom Guard, Doom Archer, Doom Trooper, Doom Warrior, Doom Knight Giants Cave: Halingka, Yintzu, Paliote, Hamrut, Kranrot Forest of Mirrors: Forest of M
This quest has no goals mapped: it is a guide task, there are no mobs in it.