Very promising! Love it! The topic is obviously not for everybody, but it can be said about any game. It would be great if the MC could choose different ways to decrease Lust other than self-flagellation. Or the degree of self-punishment could be chosen, for example he could aim to lose 30-50-70 Lust points.
Another idea is with time Mortification of the flesh could lose its effectiveness, maybe the MC becoming a masochist if he uses it too much.
Also anointment with the holy seed while dishing out punishment could be a hot scene as well, but I don't know how could it be integrated into the whole sin eating rule set.
Eagerly waiting for the next release!