Bound Hero Battle: Alm & Celica

Nino has +Res -Def with D.Speed, Scape Route and Hone attack. Distant defender 3 seal and moonbow

Tharja +Spd -hp with Darting blow, desperation, spur res, draconic aura and attack 3 seal

Robin has TA, Bowbreaker, and bonfire. +att -spd

P.Azura has TA and drive res.

Azura has to sing for Nino. Put Nino in front of the broken wall, and tharja next to her. Green mage will attack Tharja and Blue mage Nino. Later, use Sing to attack and avoid the enemies. When you kill both mages, Robin will attack Alm and Celica, with the help of the rest, with sing

(Olivia has max investment)
https://youtu.be/rzqtoe3dXpY

With buffs from Eirika, Nino can bait in the green mage and kill on your turn. P!Azura on the other side survives the lance and axe atatcked with 1HP at the end. Using Delthea + dancing to kill Alm, then Celica (take two turns including enemy phase) you can get her to kill the blue mage so Nino can kill the lance guy by Azura. On the next turn, Azura finishes off the axe flier (or he kills himself). Positioning is important, and Eirika is only there for boosts. Watch Nino's health: blue mage can kill after green mage goes down, but thanks to AI they go after Eirika instead.

Effie has good ol' Brave Lance+, Bonfire and Death Blow 3, allowing her to one-shot most units in this map.
Sigurd has his base skillset (at the moment of the challenge, I didn't have a Support skill and the Special was Miracle, so you can do this with basic Sigurd).
Performing Inigo and Lyn too have their base skillset. Well, Inigo has T. Adept 2 and Moonbow, but you won't need it as he won't fight. He just needs to dance.
Bait the Green Mage with Sigurd (beware to not draw in the Blue Mage too) and put Effie on the right, ready to get the enemies. Don't dance on her yet, she won't have to get attacked on the first turn.
As Sigurd will tank the green mage, Effie can one-shot the blue cavalier first, and, using Bonfire, the green mage too after a dance.
The blue mage will come for you from the left, and you just have to make Sigurd run a little more to the right, or tank him, your choice.
The next turn, Effie shouldn't die from the green pegasus and Celica's attacks. Use Lyn (and dance on her with Inigo, if she isn't fast enough to double) to get the Pegasus down, then shot Celica with Effie and the blue mage with Sigurd.
Now only Alm will be left, and this will be a piece of cake for your Effie.

Link: https://www.youtube.com/watch?v=J-TxncHTjos
Alfonse:
Red tomebreaker 2, ATK Seal
Sharena:
Reposition, Moonbow, Darting Blow, Wings of Mercy 2, Fortify Res 3
Performing Azura: +RES -SPD
RES Seal
Deirdre: +SPD -ATK
Glacies, Res+3