So I got the skill “Sin Strike” for Zach from an armor I bought in Aeropolis. It states that the damage is based on number of foes Zach has slain. I wonder how it exactly works, as in a fight, it damaged 83. Then Zach killed an enemy with a normal attack (damaging normal) and damaged 84. Do I have to kill them with sin strike? Is it only in that fight? Thanks in advance.