Ethel's first appearance is in front of Hell's Gate in chapter 1. She is an infamous bandit and master trap maker.
Ethel "trained" Touka in the art of trap making and survival tactics following the end of the war between the Allard Kingdon and Farom when demons terrorized the Northern continent (3 1/2 years prior to the main story line). As a result, Touka refers to her as his teacher or master.
Ethel aligns herself with the necromancers seemingly aiming for a similar goal, though she still helps Touka's group when possible.
She seems to be attached to Touka and often wonders how he's doing when they're separated.