Defeated Robin Infernal with Azura, Nino, Ryoma, and Brave Lucina. Had to do some tinkering, but I only used two whole Stamina Potions. Recreated my victory, so I can outline the strategy step by step. My turns begin when I aggro the enemy.
Turn 1: I don't have anyone strong enough to ORKO one of the Axe Fighters so I brought Nino to do severe chip damage, and I did a Sing + Draw Back to get out of the enemy's range. Lucina and Ryoma are positioned in the lower part of the corridor.
Turn 2: I make Azura and Nino retreat north. Ryoma baits and kills Robin(F) with the help of B. Lucina's buffs. Ryoma only takes minor damage, but it is enough to get in Vantage range.
Turn 3: I move Azura and Nino away from the weakened Axe Fighter. Ryoma kills that same Axe Fighter after he procs Vantage.
Turn 4: Nino ORKOs the approaching Lance fighter, and Azura sings to get Nino out of the way. Ryoma runs up to defeat the second Axe Fighter (his third kill) with the help of B. Lucina's buffs and a Moonbow proc. B. Lucina Repositions him out of harm's way.
Turn 5: Azura ended the last turn in range of a Blue Mage, but she tanks him due to her +RES nature. B. Lucina ORKOs the Blue Mage with the help of Ryoma's Hone Speed buff. Azura then walks up to ORKO the Red Mage thanks to B. Lucina's +6 Speed boost. I win.
Brave Lucina was absolutely critical when it came to scoring KOs. She allowed Ryoma to get 3 kills, and her last turn contributions were just outstanding. My whole team is strong, but I think Brave Heroes will continue to be standouts for these Hero Battles.