Almost immediately after Byleth and Marianne had celebrated their engagement, the struggle against those who slither in the dark began in earnest. Together they fought tirelessly to bring the war to an end so that Fodlan could have lasting peace. Afterwards, they left the Imperial army and were officially wed in Edmund territory. In time, the pair grew into first-rate politicians under the tutelage of Margrave Edmund himself. With the emperor's blessing, they annexed part of Riegan territory, including Derdriu, and used their influence to improve relations and expand trade with foreign nations. Their work greatly contributed to the restoration of the Empire.