Inexorable Death? Hmm...let's see. My units at that time were Lucina (Great Lord), Chrom (Great Lord), Lissa (Valkyrie reclassed from Sage), Donnel (Hero), Olivia (Swordmaster; reclass her from Dancer to Myrmidon then promote), Vaike (Warrior), Sumia (Dark Flier), Morgan (Grandmaster), Avatar (Sorcerer, reclass from Tactician to Dark Mage then promote), Severa (Hero)
What I did was send Chrom and Lucina out to rush the foes (pair Chrom with Lucina); Lucina has Galeforce so if she kills one foe she gets to act once more on that turn. I just did that while keeping Lissa and the rest of them safe.