If your critical rate is high enough, say > 50%, it strongly recommend taking Rank 2 path since you will gain 20% of Focus most of the time. You will deal more damage too, although the AOE is slightly smaller. Both paths have this effect of 100% dealing crit dmg for the next hit if you are attacked while using the skill.
Refer to the Hongmoon secret technique guide to unlock the Tier 5 skills