Responses
Is it falling in love with Eran? I had a slight suspicion, but I also thought that her sins were helping Eran. Also I'm thinking that the kings wife is human, and he married her so he wants Eran to marry her. Or his wife was human then turned into a demon. There is also her might be sin where she might travel to the underworld to save the senpai. The king might want to make her queen as well.
so i think by now all of us have figured out her sin
but am i the only one who thinks with the latest chapter that the guard figured it out?