The quest is unlocked after completing the All Hyrule, United scenario.
"With the Calamity nearing and monster attacks growing fiercer, upgrades have been ordered for forts at strategic points throughout Hyrule. Get materials to strengthen the forts' defenses."
"Resources were delivered to the forts, and the soldiers eagerly set about reinforcing their ramparts. Now they had little to fear from monstrous marauders."