The way this Build works is that you'll put Unsheathe on your Nagakiba and select the Quality Affinity to get B/B Scaling out of both Strength and Dexterity. The Greatbow has D/D Scaling with these so it makes sense to pump both for max damage with the Nagakiba and Greatbow. Additionally, keeping the Nagakiba only Physical Damage, will allow you to buff it with Bloodflame Blade.

You'll use Flame, Grant Me Strength to buff your Physical and Fire Damage by 20%, which applies to your Bow attacks as well as your Bloodflame Blade, which is excellent. It has short duration so you'll likely use it far more outside of combat than once it has begun.

Bloodflame Blade applies 40% of your Incantation Scaling to your Weapon as Fire Damage for 60 seconds, and also makes Bleed Build Up last a second or so after you stop swinging, allowing you to set Bleeding more easily on enemies, as their Bleed Bar doesn't deplete as quickly. It has a faster cast time, and you can pull it off in combat with some practice if you need to reapply it.