Very soon after Byleth and Hanneman had finished their quiet wedding ceremony, the struggle against those who slither in the dark began in earnest. The pair fought in many battles, eventually bringing true peace to Fodlan. Afterwards, they worked together to pursue Hanneman's goal to determine the workings of the Crests and to do away with the inequality caused by them. Their research resulted in magical tools which could be used even without the aid of Crests. The Father of Crestology and his spouse earned worldwide renown for devising tools that became a cornerstone of progress.