User blog comment:Miskos3/Chapter 478: Stealth, Review/@comment-1359322-20160319140344/@comment-7418318-20160319191520

His aim is to find Fairy Heart, not to kill every person in the building.

Playing around with them while they fight for all they are worth can be an effective way to shatter their confidence and thus make them more likely to give up and spill the information once the true torture starts. And in "they" Mavis is of course included, since she's the holder of the information.

I just hope that despite the rage he showed after getting the double kick he'll still stay composed enough to prevent Mavis from running off, since she is his main target.