Est

This build focuses on the fact hat she will be on a flier team, meaning she can stay in the back, supporting a flying tank, while being able to swoop in to take care of a potential threat to that tank with flier formation, while still being an economical build.

A skill is heavy blade instead of death blow in case your heavy blade seal is already in use or death blow 4 is too expensive, but the death blow 4 and heavy blade seal would the more ideal build.
B skill is flier formation to capitalize on her mobility, and since she will only be used on flier teams in order to use her weapons effect, it is the best option. Other potential options include chill def for more damage or chill atk to ensure heavy blade always prompts but those can be used on other (support) units.
C skill is ward fliers (but goad is fine depending on your team composition) to support front line tanks like a distant counter Camilla for instance. atk wave is also viable to increase her attack even further but is an inconsistent choice. Another interesting option is breath of life, since flier formation will put her adjacent to another flier, this will help heal up your front line flier.
Seal is Atk/Res bond; however, any other attack-based bond will work, since she will usually be right next to an ally thanks to flier formation. atk/res works to help her with her resistance to take on bulkier/slower dragons; atk/spd bond would work if your allies are running goad fliers, and since her bulk is far from terrible, she will be able to take a hit will quading; atk/def bond is probably the worst one to use since she is rather frail physically but she will definitely benefit when fighting against a bulkier unit she fails to KO in one engagement.

Special is glimmer to make sure she always prompts it after initiating. Galeforce is not a great option since she will likely be too far away from her allies to get her weapons buff; I would recommend galeforce if you wanted to implement a hit and run strategy and reposition allies away from danger, but even then, that would not be the best way to build her.

Best allies include distant counter Camilla for tanking and her additional support from Camillas axe, Legendary Robin (female Grima) for her tanking abilities and can take hits from archers in place of Est, and legendary Azura with flier team composition and hone atk 4.

Do you have ANY idea how hard it is to find a good Lance Flier? Aside from Cordelia, Shanna, Tana, and Catria, there aren't many quality units in this pool. Thankfully, Est, oft overlooked due to her small stature and cutesy visage, certainly makes the cut. She's armed with a potent Atk stat, excellent Res, and a weapon that is perfectly suited for a vicious offensive unit on an all-Flier squad!

Honestly, I got a slightly wonky Est, with a Res Flaw. This isn't a huge problem however, as she's common enough to eventually merge to remove any Flaw she may have, and let's be real here, 29 Res is still serviceable. A Spd Asset is rarely recommended, though it helps her deny some follow-ups on Enemy Phase, which may be crucial, especially with this awkward-yet-effective Mixed Phase build. With her weapon's refined effect in play, and a decent Spd-boosting seal, her Spd could end up in the high 30's without support. An Atk or Res Asset may be preferred, but Spd can work wonders too.

Her best weapon is clearly her Prf. While a Brave Lance may have a more reliable doubling effect, it pales in comparison to the damage potential of her refined Whitewing Spear. The refined effect does require a minimum of two or more Flier allies to be close to her, but if they have Flier Formation, this becomes rather easy to set up. The effectiveness against Armor units is also much appreciated, combined with her ability to immediately double on them. Even the trillion different Hectors in the game break into a cold sweat when they see her over the horizon. I honestly cannot think of a better weapon for Est.

Reposition is basically standard fare as far as Assists go. It works in any team aside from Armor teams with a lack of Armor March. Draw Back works well too, especially for Fliers, thanks to their unmatched maneuverability.

Since sweet lil Est can't reliably speed up her Specials, we'll need to look at either Glimmer or Moonbow, especially as she wants to focus more on Player Phase(I know I said this is a Mixed Phase, but the focus is still on Player Phase). Both will suffice. Glimmer is viable as she slightly out-damages the likes of Cherche, accounting for equivalent buffs. With enough Goad Fliers, and her weapon, her Atk skedaddles past 60, and that's without merges! Moonbow might be a bit better to guarantee some extra damage against really bulky units who don't carry a weakness to her weapon. Can't go wrong either way.

Honestly, some may prefer to give Est Death Blow, or a Brazen for her A slot. However, I like my Flying team to include a couple units who are relatively safe from archers, so I had to go with Iote's Shield here. The sad thing is, she has the second highest Def in the team, at a mere 24. They make up for their frailty by being unreasonably aggressive.

So, here's the weird bit. Vantage. Initially, I just tacked it onto her for the sake of the ol' "better than nothing" philosophy, and I didn't like her native B skill, as it doesn't help at all if she kills her target(which she usually does). I wanted to give her Flier Formation, or Drag Back/Hit and Run, but this was the only remotely useful B skill I had on hand. And now for the surprising part! It's actually not a bad pick for her, thanks to her high Atk, and decent Spd with some buffs from her weapon, and two Goad Fliers boosts. It allows her to OHKO numerous melee units quite well, before they can finish her. Not as well as some of the newer, more powerful units in the game(looking at you, Fallen Corrin), but well enough to make it a worthy choice.

Like with nearly every character in the game, the C skill is flexible. Atk Smoke can help make up for her mildly low Def and improve her overall survival, which may help alongside Vantage. Spd Smoke, or Def Smoke can help her offensively during Enemy Phase, improving her Mixed Phase potential further. Of course, Flier buffs are desirable too. I went with Goad Fliers, as the team is extremely offense-oriented.

As for the seal, I figured Atk/Spd 2 is fine. It gives her a bit of extra oomph, and helps improve her slightly lackluster Spd, allowing it to climb to a blistering 46 with an Asset, her weapon's +3 buff, and a pair of Goad Fliers. I have considered Brazen Atk/Spd, however, I cannot guarantee keeping her HP in range as Eir is also on the team, automatically providing healing support. This isn't a problem with Vantage as it mostly exists on this build as a safety net, but losing a +7/+7 is tragic. Another solution to this is Darting Stance, as it will patch up her awkward Spd stat on Enemy Phase, where it matters most. If your Iote's Shield seal is free, you can possibly give her Swift Sparrow, Kestrel Stance(a rare skill), Death Blow, Fierce Stance, Darting Stance, Steady Stance, etc. for the A slot.

Est is brimming with potential, and is only held back by her mediocre Spd and Def. Her weapon may be limited by a condition, but it is one that can be easily met. Est is a valuable asset to any all-Flier team, though she won't be able to draw out her full strength with any other team composition. Keep her safe from archers and green units(even mages, her high Res only helps so much!), and she'll charge in with the unyielding ferocity of a pink-haired loli!

The youngest White Wing finally gets a Prf and a refine (actually they all have a weapon and a refine), a rather strong refine. With her weapon granting the powerful ‘Brave’ effect and some extra stats is very deadly to face. There’s a catch though, the brave effect only activates if that are 2 or more flying allies in 2 spaces of Est, which applies pressure upon the players positioning and could lead to foes killing your units if you don’t take care. Her refine basically says, put her in a flier team for the brave effect to work.

Her build is very expensive. Which includes killing an Owain, WF!Hinoka, Brave Celica and Exalted Chrom/Walhart. Blue Flame is probably her best Special in this build, as the build completely relies on allied fliers being adjacent or in two spaces to Est. If you don’t like to invest too much into her or you simply don’t want to kill Owain for this, you can go with Draconic Aura or Dragon Fang. Luna can be an option with a Spd boon and invest into Spd with Life and Death/Swift Sparrow and Desperation, this can be used as a quad build.

Since her speed is too low to quad (base Spd at 30), I decided to go for a OHKO type of build which includes Death Blow 4. Death Blow 3 can be more of a budget friendly option, but you really need all the Attack you can get in order to successfully kill the foe and take no damage. Sturdy Blow can even be an option here if you want to reduce damage taken. Bond skills are definitely one of the other best options here, Flier Formation/Guidence has synergy with Bond Skills and Blue Flame. Atk/Spd, Atk/Def or Atk/Res bond are great options.

Chill Def is arguably one of the best skill options for an OHKO build. Desperation is another option for a different build, its better for a quad build. Investment is key in this build and I think skills like Chill Def may be expensive in terms of wasting 20k feathers to promote Walhart to then fodder him for his skill seems like a waste. Options like Hit and Run/Draw Back are other great budget skills, but this can disrupt the formation of the team.

Flier Guidence/Formation is simply there to bring fliers together this has synergy with Blue Flame and Bond Skills (If you are using them).

There is no dedicated Blue anti-dragon unit in the game. The closest you can get is Festival Ryoma with Cloud Maiougi, which requires two limited availability units. As a result, I decided to try to make a Blue anti-Dragon unit.

Budget or not, Est has the best combination of Attack, Res and Speed. Though her Speed is a bit on the lower side, it's easily remedied by a boon, QR and/or Speed refines to get out of doubling range. She may lack effective damage, but she has the potential to be a solid tank, even potentially a duelist if enough Speed is invested in her as well.

If Berkut is not available, Killer/Slaying Lance and Harmonic Lance are nice alternatives. Regarding her A-passive, I generally try to avoid using Fury on tanks, but it's still not a bad choice both offensively and defensively. For her C-passive, I only used Atk Tactic because it synergizes well with the team she is in, but it is a very flexible skill slot.

Forget the rest, use this Est. The Est archetype is so powerful, it even allows her to use legendary weapons, so she beat up Ephraim and took his lance. This gives her the attack, but more importantly the speed to double some high speed top tiers, such as Odin and Azama. Draw Back gives plenty of versatility, and works great with armors, as well as dragging your enemies into pits. Pavise is here for obvious reasons, this enhances Est's survivability by at least 3 times. Kestral Stance is more of a budget option, however, as Steady Breath is a much better option in actuality. Def Feint is used so she can do lots of damage when her less useful allies rally her. Finally, Odd Res Wave may look like a cheap option, but this skill really allows Est to tank some more hits, and she'll be ready whenever they release magical arrows. With this set, no seal is advised, as to avoid excessive damage loading by your phone leading to a game crash. At the end of the day, this is, by far, one of the best units available in the game.