Swipe your mouse in the direction indicated by the arrow. Sorry that it's quite buggy at the moment.
Sword of Souls (Shortened to SoS) Is an upcoming Hack-N-Slash First Person RPG That I'm developing. It has 8 directions of the sword, and you will swipe in the direct direction to kill an enemy, or the wrong one, or miss the timing, and you get hit, losing HP. Unfortunately, there are quite a few bugs at the moment, such as it favoring the up-right for no reason and being hard to do a down-right.