Complete the indicated chapter in Story mode to unlock the corresponding character in for Multi-player and Quick Battle modes.

Cyrus (wizard): Complete chapter 5 (Nadia). Equipped with Staff of Explosia which damage units it lands on, then explodes for more damage three turns later.
Findan (elf): Chapter 1 (Anwen). Equipped with Swift Strike which reduces charge time for all formations to 1.
Jezebeth (demon): Chapter 4 (Aidan). Equipped with Wall Crusher which explodes enemy walls and damage nearby units.
Markal (undead): Chapter 3 (Fiona). Equipped with Death March, whcih instantly charges all Elite and Champion units.
Varkas (human): Chapter 2 (Godric). Equipped with Elrath's Sword, whcih tears through first two enemy rows.