Sometime in the game a quest will become available in the Ailily guild that involves giving Arche a Mabo Curry. It does not matter if you make it or get one as a reward, but you will most likely not find one until late in the game as it is semi-rare. When you give it to her, she will say that it is going to be for Chester. Later you will get a scene in the Ailily guild that involves Arche giving the curry to Chester. Chester will get depressed and ask Arche to leave him alone for awhile. After more time you will see a scene in the Ailily plaza that involves you cheering up Chester. Tell him that "Arche didn't mean to offend you" and he will say that he knows and will thank you for cheering him up. Before he leaves he will give you the Hunter Invitation, which will allow you to change your class to Hunter.