In the Forest of Jigramunt at the starting point head East. Once you have cleared the Vassago Lv.25 and two Sniper Orc Lv.24, the Spirit Lv.19 enemy will continually respawn in pairs. They drop a ton of Evo Crystals if you kill them with one blow. Use the Brooch item to give all the experience to your I.D. This is an easy way to see all of the forms of the I.D. and to level up the ones you'll use the most.