Slotbound Factions

Every 2-star and 3-star class belongs to a faction. Different classes of one faction in your roster turn on its bonus, and two copies of one class count once. Factions work once the Crest of Alliance upgrade is bought; Arcane, Abyss, Undead and Celestial each also need their own unlock upgrade. Holy and Celestial work on all your units and Engineer on your items; every other bonus goes only to that faction's units.