Who to give Special spiral?

I have the same problem. I want to give my Helbindi Special Spiral, but I don't know if it's better for his build or not.

I would give it to your tiki, unless you're planning to merge black knight

Ophelia!
The death blow 4, special spiral, odd atk wave and blazing wind build is godly.
But if you dont, BK or zelgius would be good to. Slaying edge and s.spiral would do.

With the right kit, Black Knight (Or Zelgius) can be really good with Special Spiral. Try doing this build:

Slaying Edge+
Any Support Skill
Black Luna
Distant Counter (Or Something else if you don't have a Hector/Hrid to fodder)
Special Spiral
A Tactic, Hone, or Fortify depending on team comp
Quick Riposte, Close Defense, or Distant Defense

With this build, Black Luna's charge is reduced to 2, which Special Spiral will recharge every use.

lilina could use it too

L!Ike can use Special Spiral too.

In general, ranged units with high atk and low spd. Or if they're fast, but want to ensure specials: Users of barbed shuriken and slaying bow with a 3 cd special.

Ophelia, Lilina and Sanaki come to mind
(all +Atk) Sothe, Bladetome Mae, Micaiah, even Kagero or Kaze.

There's loads of options