Effie

Weapon: Courtly Candle+ (+Def) / Allied Lance+ (+Def) / Bridal Sunflower+ (+Def) / Effie’s Lance (+Eff)

Assist: Positional Assist / Flexible

Special: Glimmer / Ignis / Flexible

IVs: +Atk or +Def / -Spd

Passive A: Close Def 4 / Sturdy Stance 3 / Flexible

Passive B: Crafty Fighter 3 / Slick Fighter 3 / Wily Fighter 3 / Flexible

Passive C: A/D Near Save / Flexible

Sacred Seal: Steady Breath / Atk/Def Bond 3 / Flexible

• Effie’s high HP, Atk, and Def make her a solid choice for a Near Save. 
• The choice of weapon is flexible. Courtly Candle+ offers a nice boost of 5 Atk and Def while Effie’s HP is at least 50%, as well as reducing the damage from her foe’s first attack by 50% if they can follow-up attack. This pairs well with Steady Breath seal and Glimmer to potentially allow her to KO her foe before they can follow-up. There are a number of other good choices of weapon as well, including Allied Lance+, Bridal Sunflower+, and Effie’s Lance. 
• The Special is flexible, with Glimmer being a solid option that Effie can potentially activate on her first counterattack, as above. Ignis is more powerful but generally requires Effie to get hit again and counterattack again to activate. 
• The A skill and B skill are both flexible. Effie benefits from boosts to Atk and Def, sometimes Res, as well as effects that neutralize her foe’s bonuses, neutralize her penalties, slow her foe’s Special charge, and charge her own Special. Many different combinations can work so long as you are getting different benefits from the A and B skill - for example, it is not as useful to use Close Def 4 with Wily Fighter, since both provide the effect of neutralizing enemy stat bonuses, and it would be better to pair Close Def 4 with Crafty Fighter or Slick Fighter. 
• The C skill should be some variety of Near Save, the particular stat combination is not very important, with Atk and Def being arguably the best. 
• The seal is flexible. Steady Breath is a great option that provides Effie an extra +1 Special charge on every attack when her foe initiates combat, allowing her to activate 2-cooldown Specials on her first counterattack or 4-cooldown Specials on her second. Atk/Def Bond or Atk/Def Form are also good options that provide more Atk and Def when Effie is near allies. 

Weapon: Slaying Lance+ (+Res) / Courtly Candle+ (+Res) / Flexible

Assist: Positional Assist / Flexible

Special: Aegis / Sacred Cowl

IVs: +Atk or +Res / -Spd

Passive A: Distant Countering A Slot

Passive B: Hardy Fighter

Passive C: A/R Far Save / Flexible

Sacred Seal: Deflect Magic / Flexible

• Effie can also use a build with Hardy Fighter and a defensive Special to heavily reduce damage from ranged attacks while protecting her allies. This allows her to take heavily reduced damage from ranged foes and KO many of them with a counterattack due to her high Atk. 
• The choice of Special depends on the choice of weapon; Slaying Lance is best used with Aegis, as it reduces the cooldown to 2, allowing Hardy Fighter to charge it fully at the start of turn 1. This provides 75% damage reduction plus an additional 5 flat damage reduction against the first ranged attack made against Effie. Alternatively, she can use Courtly Candle with Sacred Cowl for approximately the same damage reduction, but only if the foe can follow-up attack. This also boosts her Atk and Def by 5, slightly improving damage and bulk. Skills like Deadeye and Lethality negate the damage reduction from Courtly Candle but not from Aegis or Escutcheon, so the Aegis build is safer against those foes. 
• The A slot is flexible, with Distant Counter or some variant of it being the optimal choice, with Distant Stance and Distant Storm providing useful stat boosts to Res and Atk, respectively. 
• The C slot is flexible so long as it is some variety of Far Save. 
• The seal is also flexible, but Deflect Magic is a great option that provides 80% damage reduction against any consecutive hit taken after the first from any enemy wielding a tome. This is a great check to foes like Ninja Corrin and Ascended Ishtar that could otherwise hit Effie for full damage on their second Brave hit and potentially KO her before she can counter. Deflect Missile provides the same effect against bows and daggers, but brave effects on those are somewhat less common, they often use skills like Deadeye or Lethality which ignore Deflect Missile, and Effie’s Def is much higher than her Res.