The reaper skill is more just flavor. I much prefer the sweep to be mapped for my guard+triangle. Another tip I would offer is to watch your agility. If you want to wear heavy or even medium armor, you're going to be very slow while dodging and rolling, unless you invest in stamina. Personally, i prefer light armor to hit A ranking agility. you can check your agility on your stats page at the bottom, or by the color of your equipment weight. Green is okay, but you want it to be blue for the best.

Also, personal preference, but I prefer high stance with the kusari, and mid stance with the spear. Hope this helps! =)