Erwin is the Earl of Ishtar and the grandfather of Adair. He was once married to the Duchess of Elath, with whom he had two daughters. However, twenty years ago, his wife and eldest daughter died in strange circumstances, leaving his younger daughter Cayleigh the Duchess of Elath. According to Lucille, he pressured Cayleigh to get married young to Fabian to ensure Elath's succession. According to Fabian, the two of them could never agree on who was at fault for young Cayleigh's death in childbirth.
Since his first wife's death, Erwin has remarried and had a son named Connor, aged fifteen. Connor may inherit his father's titles in-game depending on Elodie's choices.
In Week 22, Elodie can select Erwin as Adair's guardian. If Elodie is not already engaged, he will suggest that she marry his grandson.