Cordelia

• Preferred IV: +SPD / -HP or -RES
• Weapon: Firesweep Lance+
• Assist: Reposition / Flexible
• Special: Galeforce / Moonbow
• Passive A: Heavy Blade / Life and Death / Swift Sparrow
• Passive B: Chill Spd / Swordbreaker / Hit and Run 
• Passive C: Fortify Fliers / Ward Fliers / Goad Fliers
• Sacred Seal: Quickened Pulse / Heavy Blade / Guidance

Cordelia's premiere offensive option is Firesweep. This is the set which allows her to quickly kill two enemy units in the very first turn, provided she can reach the enemy team (generally done through repositions). Unfortunately, the legendary '1 turn Galeforce' relies on Heavy Blade in her A slot and Quickened Pulse in her seal slot, meaning that a sacrificial Ike is in order if you want to unleash her full potential. If that kind of sacrifice is too much for you then your typical Life and Death or Swift Sparrow will perform just fine.

Heavy Blade is also dependent on her Attack, meaning that she's less likely to proc it at her base 50 attack. Therefore, this build should only be attempted if you have some way of increasing her Attack- be it through Support, Goad Fliers, Hone Fliers, merge levels, or even a basic Hone Attack.

Galeforce is reliant on 1 turn Galeforce procs- if you'd like more damage or are unwilling to give her a Heavy Blade A slot, then you may want to take a look at Moonbow instead. With Quickened Pulse, Moonbow will activate on her second attack for bonus damage. If you're going for more sustained fights then Heavy Blade as a seal might be more of an option, as it will allow Moonbow to activate on every other hit, rather than every third hit.

Ensuring doubles is absolutely vital for this build, and nothing helps her to ensure doubles like Chill Spd in her B slot, which reduces her fastest opponent's Speed by 7, essentially granting Cordelia +7 Speed every time she engages with the fastest opponent on the enemy team. For a more budget option, Cordelia can take Swordbreaker instead, since the units she has the most trouble doubling are sword units such as Ayra, Mia, and Hana. Hit and Run is an option to retreat if you're not using Galeforce- running Hit and Run with Galeforce is questionable as it positions you further away from the enemy team and limits your second-turn capabilities if you wanted to go on the offensive again.

Your choice of C slot is variable, though Cordelia absolutely does not need defensive buffs, so she's happy to freely give them out to her more tanky teammates in return for a valuable Hone or Goad fliers from them. Alternatively, you can stack Goad Fliers across your entire team for a large Atk/Spd boost.

• Preferred IV: +SPD or +ATK / -HP or -RES
• Weapon: Brave Lance+
• Assist: Reposition / Flexible
• Special: Moonbow / Luna
• Passive A: Life and Death / Death Blow / Swift Sparrow
• Passive B: Hit and Run / Chill Spd / Drag Back
• Passive C: Fortify Fliers / Ward Fliers / Goad Fliers
• Sacred Seal: Quickened Pulse / Heavy Blade / Speed +3

A slightly cheaper but still very effective set. Brave Cordelia can be built to attack 2x or 4x, depending on your IVs and flier buffs. If you're using a +ATK Cordelia, then Death Blow/Moonbow/Quickened Pulse gives consistent upfront damage, allowing her to dish out big numbers on her first attack. A Heavy Blade seal should be considered for more regular Moonbow procs if you have flier buffs or if you're confident in her Attack numbers (she will hit 52 Attack unbuffed with Death Blow, 58 Attack with Hone Fliers buff).

If using a +SPD Cordelia, then Life and Death/Luna/Speed+3 is also an option. This raises her Speed to a natural 41 with her Brave Lance, allowing her to quad most slower units and activate a guaranteed Luna. This only improves with flier buffs, as she'll be capable of reaching 47 Speed.

The rest of her set is similar to her Firesweep build in utility, as she can incorporate Chill Spd to try and ensure quad attacks, or simply utilize Hit and Run to retreat back into her team after she's finished off an enemy unit.

• Preferred IV: +SPD / -HP or -RES
• Weapon:Slaying Lance (+Spd)
• Assist: Reposition / Flexible
• Special: Luna / Galeforce
• Passive A: Swift Sparrow / Life and Death
• Passive B: Desperation
• Passive C: Fortify Fliers / Ward Fliers / Goad Fliers
• Sacred Seal: Heavy Blade

Cordelia is also capable of utilizing a Slaying Lance build for something of a pseudo-brave set in utility. The idea here is to knock Cordelia into Desperation range in her first engagement, and then for every initiation afterward, she attacks twice, proccing her Heavy Blade seal for Luna damage on every initiation that she can double and proc Heavy Blade. 

She doesn't have a retreat option with this build, so it's up to her teammates to get her out if she dives into enemy range, but this set allows for her to push for high Speed, high damage engagements which ultimately do more damage than the previous two builds, albeit at the cost of some survivability.