Fir

{(Special Spiral 3 is her B slot It wont let me put it as so)}

Atk Ploy: Helps her live most physical hits better and take Zero damage from non-Blue mages.

Spd Ploy: Just as good as Atk Ploy helps her team more than her.

Def Ploy: Needed to help her 'MASSIVE' 25 Atk stat (or 29 with a boon) helps secure kills with her Res based special

Merge +6
A balance and useful Fir build. A bit expensive but it can sure surprise people in Arena. (Not highly recommended for F2P players, unless they like Fir too)

Build using fairly common units for Skill Inheritance. Ardent Sacrifice from Florina/Rebecca, Iceberg from Niles/Shanna, Fury from Hinata, Desperation from Shanna, Def Ploy from F2P Arvis.

EDIT: I switched Desperation to Wrath because I had the opportunity. Highly recommend if the option is available to you.

Fury gives a boost to all of her stats. This gives her a much needed boost in attack and having more speed to double and avoid doubles herself is a very nice perk to have. The extra defense doesn't hurt to have and the extra resistance allows her to utilize ploy skills as well as boost the additional damage from her special.

Desperation allows her to attack consecutively with two ways to reach the Desperation range. Fury allows her to reach the range in two encounters. Ardent Sacrifice allows her to activate it while healing a teammate. With the optional HP+3 Seal, Fir retains 3 additional hit points which could very well be the difference in whether Fir survives certain encounters.

EDIT: When using Wrath over Desperation Fir's doubles will no longer be consecutive. However, this boosts her damage tremendously by +10 with her already strong Iceberg.

Def Ploy is almost always going to activate with Fir's 37 resistance. Def Ploy allows Fir to do more damage both with and without special activation.

Spd Ploy nearly ensures Fir will double foes and avoid any doubles from unmerged units.

Iceberg is a great special which Fir can proc more often because of Nameless Blade's -1 cooldown count.

For this build I strongly recommend the special refine as it gives her sword a Wo Dao effect along with a decreased special cooldown.

Player phase nuke which adds at least +30 damage per special activation thanks to glimmer/nameless blade/wrath if Fir is under the house threshold. -HP bane is to lower the amount of furies it takes to activate wrath. Quickened pulse will allow her to activate glimmer immediately since she will be at full health. While low in attack, odd attack wave and the specials should balance out the damage

-Preferred IV: +ATK / -HP or -RES
-Weapon: Nameless Blade (+Eff)
-Assist: Reposition/ Ardent Sacrifice
-Special: Luna/ Moonbow
Passive A: Life and Death/ Fury
Passive B: Desperation/Swordbreaker
Passive C: Hone Atk/ Flexible
Sacred Seal: Atk +3

This set was created with the idea of using Fir as an offensive, player-phase unit. Yes, there might much better choices than her due to the fact that she has an extremely low base Atk, but giving her the right kit, she is able to demolish most of the units in the game.

The one thing which is necessary so that this build can be effective is that she must have a +Atk IV. Although this doesn't seem like that big of a deal, since she can be a common sword unit in summonings, it is still kinda tedious to deal with since you have to use up 20k feathers to get her to 5 stars (unless you're lucky enough to summon her at 5 stars with the right IVs). But once she has the right IVs and you give her the Nameless Blade (+Eff), Life & Death 3 and Attack +3 Sacred Seal, Fir can reach 53 Atk and 41 Spd, which is actually better than a neutral IV Mia, whose stats would be Atk 51, Spd 40. Having these stats, along with Swordbreaker, Fir can outspeed and practically OHKO the majority of the units in the game.

Now, because of Life and Death 3 decreasing her Res, you can no longer run Iceberg or Glacies as her special. Therefore, Luna or Moonbow are good options since both of them have low cool downs and Nameless Blade help them have even lower cooldowns and dish out more damage. Draconic Aura might be a good option too due to her high attack stat of 53.

For her B slot, Desperation is a great option since it gives her more survivability when facing opponents at low health. Swordbreaker is a good option too since it guarantees more KOs against faster sword units such as Ayra, Mia or even Athena; it practically gives her more dominance over other sword users, but it's more risky since it won't allow her to survive a second fight (she would have to rely extremely on a healer). I recommend using Firesweep Sword+ if you wish to run Swordbreaker, which is still a really good set for Fir.

I gave her Hone Atk for her Slot C, but this can be replaced by practically anything that fits the most with the team where the player wishes to add her. Perhaps Threaten Def or Spd might work as well, but again, it's the choice of the player.