Lord of Fire
The Great Conqueror
You didn't explain what you do after the special episodes...You recruit Warlords the same way you do when you're recruiting warlords in main story.
so defeat the warlord within 4 turns, super effective move, or without getting hit. And it must be defeated by another Warlord. Like I defeated Oichi's Jigglypuff with my Gracia's Psybeam within 4 turns and manage to recruit her.