Subaki

With a defense boon and defense refine, Subaki reaches a staggering 42 defense. His HP is also very good for a flier, so with those traits alone he'd be a flying physical wall comparable to Beruka. But he has one winning aspect over her. His impressive 35 base speed.
With a speed tier like that, Subaki negates MANY doubles (With minimal support) from high threat reds like Mia and Ayra, and still take next to no damage if any at all.

For this build we're emphasizing his physical walling prowess, longevity, and semi-unique ability to function equally well in both phases.

For the weapon, Slaying lance is chosen to make proccing specials faster, which is helpful with that monster Ignis he packs.

Swap comes default with Subaki and is great for putting him between threats and allies.

For A skill, since we want to keep him from being locked to one phase, Brazen Atk/Def is chosen for improving his admittedly lacking attack, and further bolstering his impressive defense. A single stat boosting A skill can also be used if you want. Fury however isn't advised as making a wall unit that constantly loses HP screws them over pretty hard.

For B Renewal is chosen as it's one of the few B skills that directly benefits pure bulk sets, naturally granting healing without a healer. Guard is also an option if you wish to prevent specials from just ripping through him.

On C Hone Fliers is used to grant offense to his team, since he already doesn't really gain as much benefit himself from trying too hard trying to fix that attack, but if you have another ally with Hone he's a good option to have as the second unit with it. He also can work well on mixed teams using Guidance and Tactics.

For the Seal he uses Iotes to keep archers from denting him, leaving his only weakness as magic. Although Guidance and tactics seals are also good if you want to go mixed teams.

All in all Subaki makes for a great physical wall on flier teams that is often overlooked due to his wet noodle attack stat and value as Quick Riposte fodder.

Use Subaki and I promise you'll be surprised.

My personal Subaki build that also functions as a mixed tank... kinda.
You see, his combination of speed and res makes it so that he lives a good percentage of mages (he still dies to a lot of green mages tho).

Wep- Simple. The slaying effect is useful because his Ignis is his only way of dealing significant damage. Refine boosts Ignis damage.
Assist- Draw Back, cause I like using it on fliers for some reason. Just use Reposition, to be honest.
Special- Ignis for big damage, because he rarely deals any.
A- This skill may be kind of awkward, but it makes sense. The attack drop is negligible because his attack is already so low. In return, he tanks many dragons and whatever armor unit is thrown at him. Handful of mages too.
B- Guard is to protect him from Black Lunas, from Aethers, and whatever other specials you can think of. Unfortunately, he'll be able to take enough damage to get out of range, but this is enough to block big threats from charging specials, while also charging your own frim every little *dink* you take.
C- Honestly, I use Goad Fliers cause I don't have any Hone Fliers fodder. I do have to say that Atk Smoke and Spd Smoke work well if you don't use him in non flier teams.
Seal- Simple. Archers (even though he can tank them easily) can still kill him with their cute Brave Bow sets. Without this, he will simply crumble against any L!Lyns, and L!Alm will still manage to deal a semblance of damage to him, even without it, but at least he won't get one-shot.

Juice his defenses up with buffers, and slow enemies down so that he can put his speed to use.

Tannenboom makes him a quick tank who excels in defence. Qr is there as while he is not in brazen range he cannot reliable double but the moment he hits 80% hp he has 52/44/41/21 stat spread on initiation. He is normally ran in a flier emblem setting where he shines. This build is high investment but i like the unit.

The Iote's Shield SS frees up Subaki's A slot and makes him truly the tank of the flier emblem team, a boost that the team desperately needed. His A slot is free of use and could mean running something like Distant Counter to stop ranged heroes in their tracks, but be forewarned about his low res, as green mages will waste him with little effort.

(A build for my favorite Fates character. Aiming for +10 five star merged to make it better for myself) A set with decent enough attack that becomes even higher with death blow. Bonfire always activates when under attack, dishing out a hefty 20 damage. It only gets better with flier buffs. This set makes Subaki perfect (pun intended) for both player and enemy phase. The stats are added by two because summoner support was considered in, as well as the defense +3 seal.