|With her naturally high speed, Corrin can utilize her native weapon quite well.
Her optimal boon is +Atk due to it being a super boon, giving her +4 atk rather than the normal +3. However, other boons such as +Def and +Spd are also acceptable alternatives. Because this build is focused on being a physical sponge, -Res is her optimal bane, though -HP is also acceptable.
Dark Breath+ is the weapon of choice in this build, allowing Corrin to capitalize on her first combat, which will generally be in her advantage, and apply a large debuff to the enemy which allows her to much better tank the rest of the enemies when they come into range in the enemy phase. +Spd is the best refine for the weapon, as it will better allow her to double enemies if she chose to initiate and avoid doubles.
Reposition is a powerful assist for enemy phase tanky units, but other options such as dual rallies are also very strong.
Moonbow is a strong option for Corrin, as it'll allow her to cut through tanky enemy units on a low cooldown on her first combat, as its cooldown is not enhanced by something like Lightning Breath+. Alternately, one can use Bonfire to empower Corrin's second combat phase.
Distant Counter is important to the build, as it is not build into Dark Breath+.
Quick Riposte 3 enhances Corrin's enemy phase prowess, allowing her to always be able to hit back twice.
Alternately, Wrath 3 is a strong B skill for her if one chooses to rely on the Dark Breath+ debuff in addition her natural speed to double opponents. It further increases her kill potential on targets that she normally wouldn't be able to kill, in addition to opening up the use of higher cooldown skills such as Aether if one wishes to do so.
Hone Atk 3 is Corrin's natural C skill and is very good, but can be changed to suite the requirements of her team. Other common C skills are other hones/spurs, Panic Ploy 3, or smokes.
Depending on what threats you need Corrin stand up to, her S slot can change between Distant Def 3, making her more durable against ranged threats, or Close Def 3 which makes her more durable against melee threats.
Alternately, if one chooses to go Wrath 3, the Quick Riposte 3 seal becomes a solid option to allow Corrin to keep up her enemy phase prowess, albeit at the cost of some tankiness.