You need to defeat a scary monster to make a cute Magical Girl join your team. This guide will show you how to defeat Nerthus and recruit Mellore in Eiyuden Chronicle: Hundred Heroes.
Eiyuden Chronicle Mellore Recruitment Guide
After Nowa finishes his first job in the game, Ymir assigns him to recruit more people for the squad. The first recruitable person is already in Eltisweiss, your starting city. She is Mellore, a little Magical Girl. After you tell her where Redthroat Ridge is, you decide to follow her and help her.