Bound Hero Battle: Ephraim & Eirika

Make sure Nowi has Sword Breaker.
Fae with Lightning Breath helps a ton too.

Spec:

Hector (+Def/-Res)
DC, Lancebreaker 1, Threaten Def 2, Fortify Res Seal
Armads, Swap, Bonfire

Brave Lyn (Neutral)
Swift Strike 2, Desperation 3, Atk Smoke 3, Speed Seal
Mulagir, Reposition, Draconic Aura

Azura (+HP/-Spd)
Speed+3, Wings of Mercy 2, Fortify Def 3, Spur Def Seal
Sapphire Lance+, Sing, Luna

Genny (+HP/-Atk)
Speed+3, Wrathful Staff 3, Hone Atk 3, Atk Ploy Seal
Assault, Physic, Imbue

Ally Supports:
A -- Hector w/ Lyn (Res/Def/Spd+2)
B -- Azura w/ Genny (Res/Def+2)

Summoner Support:
B -- Azura (HP+4, Res/Def+2)

Turns Taken: 5

Which and who defeated what (in order):
1. Lyn -> Blue Mage
2. Lyn -> Green Cavalier
3. Lyn -> Red Cavalier
4. Hector -> Ephraim
5. Genny + Hector -> Eirika
6. Azura + Lyn -> Thief

Turn 1: Preparation
| x | 1 | 2 |
| 3 | 4 | x |

Lyn [2] destroys the nearest wall on top of Hector [1] and he swapped position with her to let her soak on res buff from him and hone atk from Genny [4].

Turn 2: Baiting
Lyn moves 2 spaces up, attaching herself right at the end of the wall to bait the blue mage. Hector moves left to [1], get danced (sing?) by Azura and moves up to provide further res buff from support to Lyn. Genny moved to Hector earlier position on the right [2]. During the enemy phase, the blue mage will attack Lyn and left her <50% HP. Lyn can't double the mage, but it's okay. Enemies will pursue from top (Ephraim and Eirika) and the rest will come from the left side. Ephraim will pivot to arrive right at Lyn's face.

Turn 3: First Kill
Use Lyn to finish off the blue mage, then Hector will swap his position with her to tank Ephraim. At this situation, Eirika can't yet reach Hector so he will only deal with Ephraim alone later. Genny should heal Lyn from where she is (+8HP) and Azura will sing her out of the single danger zone behind Hector. Lyn moves to the position below Genny to receive on hone atk buff for the next turn. During the enemy phase, Hector will tank Ephraim's special once and hit back twice. Fury will proc on Ephraim, leaving him with a small amount of HP. Eirika will finally arrive at her side. The enemies on the left will come closer but should not be able to hit anything.

Turn 4: Sweep
Lyn should still be under desperation zone at <75%. Moves her to double the green cavalier first, readying her special to proc. Azura will then refresh her and have Lyn attack the red cavalier, without a special she won't be able to ORKO it (missing 3-4 damage). With this the two big threats from the left field are gone and most importantly, the thief will have its attack reduced by Atk Smoke (38->31). The reason Lyn needs a speed seal here is to prevent her from getting doubled by the thief at the next turn (43-38=5, so a +1 negates it). The Atk Smoke itself is needed to prevent Azura and Genny from dying to double as their speed is far below what's needed. On the top side, Hector's special will proc and use it to finish Ephraim, Genny will then heal him (+18HP) to let him survive Eirika's moonbow+attack next turn. In the enemy phase, the thief will attack Azura as she's the only melee that won't counter and reduce her health down to half. Eirika will nearly down Hector and dragged her back 1 space to the north.

Turn 5: Finishing
Hector won't be able to KO Eirika.
Lyn won't be able to KO the thief.
So Genny should first weaken Eirika with a ranged attack, and similarly, Azura should do the same with the thief.

If you decide or are able to run with this set up, the most important skills to SI are:
Lyn: Desperation 3
Hector: Lancebreaker (even level 1), Swap
Genny: Hone Atk 3

Supports don't really make a huge contribution other than the baiting part to slightly reduce the blue mage's attack, so it's not necessary.

/u/nibelung25

This team cleaned house. I had Hector tank the thief and the mages (note he had Spur Atk, Drive Atk, AND S support supporting him), let my Lucina kill the Sword Cav, from there I backed up and let my Bridelia finish off Ephraim with her S-support boost from Delthea, then I weakened Eirika and finished her off with Lucina's Aether. Easiest BHB BY FAR.

Must Have:

Xander: Siegfried, Reposition (SI from Barst, Selena), Armored Blow 3 (if you have Vantage 3 and Bonfire this battle is more easy)

Elise: Rehabilitate (Lissa 4*), Hone Cavalry (Gunther 4*)

Lyn: Her skill (No SI)

Azura: Sing (if you have Threaten Defense is more easy)

Youtube video (ITA): https://www.youtube.com/watch?v=QhWOglLCavM

Here's a video of how I did it since it would be easier to watch this than to make a wall of text.

https://www.youtube.com/watch?v=5DHiSuLA2Cg