Optimal Special Fighter User

Well what's his IVs. If he's good on IVs I suggest keeping him. Unless you're really insisting on giving one of those characters SF

Considerations:
L.Tiki: mainly to be considered if you have +spd IV. Otherwise I find her just a touch slow, unless you have some plan with hone armour or something, but I think she wants to focus on receiving armour march.
H.Myrrh mainly if you're willing to let her hog your QR seal
LA Hector I think prefers special spiral.

I personally like it on H!Myrrh (partially because it fits the guard theme of the H!Units, but she's a true Spooky Monster with it).

Spirit Breath +Special Fighter +QR seal - Doubling all over the place while speed charging her special and denying the enemy.

B!Ephraim and L!Tiki are easily the best options since they don't rely on seals (Garm for follow-ups and natural speed for follow-ups). Halloween Myrrh is great if you're willing to constantly run the QR-3 seal on her. VHector is meh even if not that bad.