Defender's Emblem

A Defender’s Emblem opens one more squad slot for your battles. You hand it over in the Barracks, where the answer Unlock Squad Slot costs one emblem; once the Barracks has the most slots it can have, that answer no longer appears. Battles give emblems as rewards.

Your first comes from winning Break Through to the Port in First… Sludge?, along with 6 Zombie goo and 4 Town Gratitude. Only four battles give one — Break Through to the Port, Eastern Districts: Active Scouting, Central Districts Purge: Part I and Break Through to the Bathhouse Basement — and four is exactly the number of squad slots.