The Nikana Prime is one of those weapons which really benefits from the Blood Rush / Body Count combo. This build is meant to take advantage of this combo to encroach on red-crit territory through a massive melee combo.
North Wind is the flex mod. It’s an all-around solid choice, along with Molten Impact and the choice depends on whether you’d like to do more damage to alloy armor and have a slow proc, or have another chance at a damaging proc (fire) and do more damage to the cloned flesh.
Buzz Kill is highly recommended against infested and for 4x CP groups. Remember, slash is king.
Organ Shatter is another great choice and will really shine once you begin to preform red-crits. If you’re likely to reset your counter like in Defense, I would not recommend Organ shatter. Bring it for Survival or maybe Excavation.
The last mod I’ll mention for that slot is Primed Reach if you like it.
Life Strike’s rank is personal preference but I find it to be an extremely valuable mod and I use it on all my melee weapons.
If you know you will only be using North Wind instead of any other flex mod, this build will require 0 forma. Simple place North Wind in the Vazarin (D) slot.
The same applies for Viral damage type builds.