Seliph

Deflect Magic is pretty good on him... I'm looking at you, Gamepress! He's +10 w/ Summoner Support.
He rarely dies with the good ol' Steady Breath+Aether combo. Mages do shockingly little to him. Ex: Ishtar in lunatic story maps does 30 damage to him when he's unbuffed, AND Ishtar has her Odd Atk Wave buff AND her Moonbow procs.
Also there's a reason I chose -HP rather than -Spd. 30 Spd plus a visible Spd buff is enough to avoid key double attacks from some strong units, so the payoff is much better than 3 extra HP.

This Seliph set is a primarily EP focused duelist set for physical units and dragons. The idea here is to return a Wrath boosted Iceberg using the boosts from Warding Breath and Close Def. With this set he has 88 Physical bulk and 87 Magical Bulk on EP. Atk Smoke is meant to add to his bulk by lowering the enemies Atk by -7. Wrath is also useful here in that it also charges your special outside of combat, so you can also do some PP action as well. Seliph wants a boon in his Res to bring his res up to more respectable levels, while having a bane in his Spd doesn't affect his match ups too much. Divine Tyrfing is also a (budget) option for him, but is not as useful due to not having -1 CD as an effect and thus returning an Iceberg every counter, not to mention the Res boost from a refined Slaying Edge being more useful and higher. Overall, Seliph may be outclassed as a sword user in some aspects, but can find a respectable niche as a mixed tank duelist

This Seliph is pretty self explanatory, he tanks everything, every phase. His plus defense iv help boost his mediocre defensive stat while the minus hp prevents from taking away from his already disappointing speed stat allowing him to prevent being doubled by slow, heavy hitting melee units. Divine Tyrfing boosts his resistance as well as his magic tanking capabilities. Brazen Def/Res further increases both of his defensive capabilities. Wrath and Aether help keep Seliph at the very top of the brazen range, enabling him to always be at peak performance. Attack Smoke's AOE debuff further compliments his tanking abilities by weakening the surrounding enemies attack after any combat. Finally deflect magic ensures that Seliph is a hardy mage tank able to survive hits even from Reinhardt.

This build with or without Summoner Support allows Seliph to perform as a enemy phase mixed tank, being able tank the strongest hits even from Blue Tome units like a Life and Death +ATK Delthea and Reinhardt, and tank reliably against Axe and decent amount of Sword units like Ryoma and Ike, but has trouble against units like Ayra and Mia if he doesn't have his special ready. He also has decent match ups against dragons, as long as he is the one being attacked.

Your aim in this build is to tank a mage on enemy phase, and counter on player phase with stat/special buffs.

A Spd bane is best for this build, because you want to be double by enemy mages any time your attacked. When doubled by a mage, you charge your special by 4, plus bonus 4 Res from Warding Breath, and damage is reduced by 50% on attack 1, and 80% on attack 2+. You hope to be just under 75% HP at the start of the next turn, meaning Aether is charged, and you gain +6 Atk if it's an odd numbered turn. With an Atk Boon, this means your next attack will be:
[ 59Atk - (EnemyDef * .5) +10 {Heal 50% Dmg Dealt} ]
Plenty to destroy the enemy, and also recover all your HP, ready to tank another mage.

Lastly, the Assist Skill is flexible, but I prefer Reciprocal Aid, so that even if the enemy team doesn't run any mages, he can be used as an HP refresh for an ally.