Corrin (M)

Assets: Res
Weapon: Yato(+Eff)
Assist: Reposition / Swap / Flexible
Special: Iceberg / Glacies / Moonbow / Flexible
A: Fury 3
B: Axebreaker 3 / Swordbreaker 3 / Flexible
C: Flexible
Seal: Drive Atk / Flexible

+10 merges, and +5 dragonflowers. I expect him to be a supporter for his love, but his good statline makes him the capable swordsman and also attract Chill effects as well.

I think that +Res is the best asset, because of his high overall statline. First it is the superboon so it is a worthy pick. Also, with +Res asset, he can have up to 39 on both Def and Res if you fully merge him and also put ten dragonflowers. It is not only allows him to attract Chill Res, but also helps him to fight against dragons and tank red/green mages in a pinch.

Effect refine of Yato is a great option, for it increases the effectiveness of himself and also his love. +2 to all four stats without any feedback damage means you can get Fury 2 for free, so it is not a bad deal as you might think at a first glance. It also means you have not much a reasons to refine it with stat increasement type too. Because m! Corrin's statline is quite balanced, increase all four stats simultaneously just makes him an all-rounder and there is not much a merit to making him a specialized bruiser - and you better try with the other units if you want a swordsperson with specialized at some situation.

+4 stat(with support bonus) to his love is an another advantage, and it is one of the unique signature ability in FEH. Honestly, that's the REASON to pick m! Corrin, unless you have played Fates and like him very much already. It is the most powerful buffing ability on the game too, although it only targets one specific type of hero you have designated as his partner. You may designate one lover of him or you can change his support as you want.

Assist skill is largely depend on your taste, although as a melee infantry unit m! Corrin usually works better with Reposition/Swap than Draw Back, as his peers does. I suggest you to have the diffrent assist skill with his partner, though, for you may react to the broader sitaution if one of your unit have Reposition and one another have Swap. And, if his partner is a ranged unit, you will know that Reposition would be better than Swap in the most times.

If you want a 2 cooldown special, Moonbow is what you want. Because you rarely want to use him as the tip of the spear and he is not expected to have Heavy/Flashing Blade, it is unlikely that he will have much times to charge his skill. So, basically Moonbow is the most useful pick when you want a damage bump.

But, as you know Moonbow is not so powerful, and he is tough enough to survive at least one combat against most green units(or even against moderate blues sometimes!), so you may expect some hits before try to finish off your enemy. In this case, I suggest 'Boosts damage by 50%/80% of unit's Def/Res groups. For me, it seems that Iceberg and Glacies seems better for the most players, for you may put him the Light Blessing and use him with Eir(who increases Res on her season and everyone can get her for free). But it is largely depends on your teammates. If you put him the other Blessing and your prefered Legendary/Mythic Hero buffs Def, you better take Bonfire/Ignis instead. If you have neither one, they are virtually same unless he gets the buff/debuff(because both his Def and Res are same) so just take the best nametag of your taste.

Fury 3 is one of the popular budget option on A skills groups, but it is very effective skill on him as well. As I said above, m! Corrin's statline is balanced. Normally most gamers in FEH needs the specialized stats rather than the spread one. But you already have the balanced stat boost from Yato, and why not for the another one? Low overall stats means he don't have the duty to resolve, but high overall stats means he can do most things expected for his class. You can just be a jack of all trade, but you don't also need to become a master of none. Higher overall statline means he is more likely to be targeted by Chill effects and you can use him for the reserve combatant better, so it is not a bad deal either. Also the other popular picks - Swift Sparrow, Life and Death, Brazens, Fortress, or even expensive Breath or Distant Counter! - are works well too. After all A skills are not there for helping his primary reason(to buff his love) and there for helps himself when he needs to fight, so it is largely depend on your taste and team composition.

B skills are also largely depends on your taste. But, usually m! Corrin is expected to support blue units because he is a red unit, so you better make him deal with the greens for his love. In my experience, usually you better needs for either Axe/Green Tome breakers. Although Swordbreaker is quite handy, but there are some nasty and disgusting green enemies such as Surtr, so Axebreaker is the most useful and also cheap one. Also, usually axe have more useful armor units(who are expected to be quite durable) than the other colors, so something to dispatch green(and a tool for punch through Wary Fighter or stop the following attack of Bold/Vengeful Figter) would be what you need in the most times as well. But, if you have the another good solutions for the durable green enemies, you better take the others such as Wrath. If you just want to nullify Fighters then Null C-Disrupt also works well, and with his good Spd he is expected to be double against such slowcows, but you must not forget that m! Corrin is a supporter first and foremost - you better put the best combat equipments what you can afford to the unit what he want to support first, then we can talk. Other than buff elements, you better take the budget options on him while fully arms your best fighter.

For C skills AND seals, I suggest you to have either of Drives. To protect him from the enemies' attraction, you better make 1 space between him and his partner, and Spur is useless in such positions. Unless you put Distant Counter on him and make his partner counterattack against most foe, I don't recommend you to learn Spur Def/Res and stick both of them together. The type of Drive is largely depends on your taste, and more importantly, his partner. If his partner have very low Spd and the partner have the solution for the low Spd, then Drive Spd on him have really no use, for example. Else, if you want his partner to be a mixed tank but the partner have lower Def, then Drive Def 2 can help his partner. If his partner is good at the most things but doesn't hit hard, then Drive Atk 2 is what you want.

Also, because you can inherit the other Drives by spend a 4☆ hero that can be on the summoning, I recommend you to take Drive Atk 2(the only Drive that requires the grail when I wrote this) as the seal rather than C skill unless you want two of them at once.

You may take Tactics too, but it forces you to make the team fit with the skill. I don't recommend Close/Distant Guard, for it only works on the enemy phase. Unless his partner is mainly aim for counterkills, you better avoid it.

Also, it is possible that you can make multiple m! Corrin and circle his partner to doubles the benefit from Yato, although it would be not so easy to make the team for it.

Powerful blue units are the best candidate for his support, but you may take the mediocre unit and want to use it with powerful stat increasement. Other than blue units, Caineghis seems the most pick for his support, for you can throw him and forget.

[Stats are at 0 merges and Dragonflowers, but with Yato refine and Life and Death stats]

[if a bane is required, then Res is probably the best stat for this build]

This particular build is all about capitalizing on Corrin’s average-ish Spd stat—as a call back to Yato’s original effect before refining.

Yato remains, because its utility can not be understated—+2 to all stats permanently and without penalty is amazing. Here, instead of utilizing the effect refine, Yato is refined for extra Spd. His assist skill can be changed, but I prefer Swap so he stays within range of his allies after combat. His special is also customizable—I chose Glimmer because of its low CD.

Life and Death reduces Corrin’s bulk, but compensates it with higher Spd and Atk. These two ensure that Corrin kills a foe within one round of combat and avoids as many doubles as possible. Null Follow-Up is to deal with Armored units with Fighter skills who ordinarily wouldn’t be able to land more than one hit on Corrin.

Infantry Pulse is also customizable. Though Corrin’s allies are enemy phase units and so Infantry Breath would suit their needs better, Infantry Pulse allows them to unleash their specials within the first turn and get the round over with faster. Panic Ploy is to take advantage of Corrin’s high HP, and to counter team compositions with that run visible buffs like Hone/Fortify, Rally, or Tactics.

A pure support build. Functions especially well when paired with blade tome/bonus doubler teammates.

Preferred IV: +RES / -HP
* +RES is a super boon on Corrin (M) and helps to balance his defensive stats. -HP is taken to avoid lowering any of his other stats that may serve to soak any chill skills the opposing team may have.

Weapon: Yato (+Eff)
* In addition to providing Corrin (M) with personal buffs to himself, Yato (+Eff) will also boost the stats of his support partner if they are within two spaces of each other.

Assist: Reposition / Shove / Flexible
* Movement skills are used to take advantage of any link skills Corrin (M) possesses. Reposition and Swap in particular are helpful for moving his teammates while remaining within optimal ally support distance.

* Shove is also of note. It will allow Corrin (M) to stay within range for giving tactics, Yato (+Eff), and ally support buffs while not interfering with beast transformations or solo skill users.

Special: Moonbow / Noontime
* Corrin (M) will likely not see too much combat while ferrying teammates around the field, but on the off chance he does a low charge special may prove useful. Moonbow is handy for getting that extra amount of damage, while Noontime can help with sustain.

Passive A: Fury 4 / Fury 3
*

Passive B: Spd/Res Link 3
*

Passive C: Atk Tactic 3
*

Sacred Seal: Def Tactic 3
*

This is a tanky support set up specifically made to ensure Corrin's survival while buffing his supported ally, as such Fortress Def/Res 3 is essential for this build. B slot is rather flexible, but any of the Link skills are good so that he can buff himself for potential combat and it depends on his ally, same goes for his C and Sacred seal slot.

This is the set that I’m currently running on my Corrin and it’s working really well so I’ve decided to share it.

Despite his defense bane, he’s actually a really good enemy phase unit due to Yato’s weapon refinement which bringing his bane up by +4(or 6, if you count the +2 to Atk/Spd/Def/Res) and close defense. Brazen Atk/Spd 3 (you can get it from Linus with the grails btw) works well with Threaten Defense 3 so you can be able to defeat the enemy during your next player phase, or wait another enemy phase to get the +6 Def/Res with Vantage 3 Incase you need to mitigate the damage taken.