This manga rocks!! I think that the dark king might not have an ability because he even used what seems to be a regular sword. I think that "spirit attacking" or what have you is a logia stopper. Maybe its like an uber concentration where he is attacking very forcefully to an area versus a target and since logia bodies take up space of the targeted area they take damage because the attack is indirectly effecting them. So it probably takes forethought to fight logias physically.