To slow down an enemy, one of the best elements was ice. It could even slow the enemy's time reaction since he would be too focused on the cold to notice an upcoming attack.
And Eden was aiming for that. Since the boss was too fast for him to attack it properly, the only way would be to slow it down. And what best than ice for that.
'You could have use illusion too, you know?' Kye said just before the magic circle was ready.
'Illusion takes too much time to create, whereas ice magic is spontaneous for me.' Eden answered. It was clear just with his statement that he was greater with ice magic than any other element he could possibly think of.
Once the magic circle was ready, Eden activated it and sent the arrow to the dragonfly that wasn't moving much. He even added an auto-trajectory to the arrow to touch the boss without any chance of missing.
