-Erica hated MC before even asking why he killed his servants.
The Stokes have a really bad reputation for treating commoners as livestock. That's the complete opposite to how the Sumeragi handle things. This actually showed in how Erica's parents apologised to Erica for forcing her to marry into such a family, to save the Sumeragi domain. It's just that hearing rumours/reports about it, no matter how much, is different from actually listening to Harold personally boast about it. That was the last straw for her.
-The spy-girl thinks he noticed Erica when telling the story of how he had not killed servants - because he noticed her hiding in the forest. But for some reason, they still act as if he doesn't know they know.
That's a weird thing I also addressed at one point, from a different point of view (that a person would feel the most safe in their own room/office, as opposite to a forest), but I actually hadn't noticed that detail you stated here. But then again, even if Yuno's theory was correct, the Sumeragi still couldn't bring it up as long as Harold didn't do it first. It would be like both parties pretending for the sake of status quo. After all this time, though, one would think Yuno had abandoned her theory.
-The girl who is portrayed as an angel by the author can't even be sincere to her beloved. That's okay; I don't mind characters being selfish manipulators. I do mind though when they are portrayed as kind sweethearts for the audience. Seriously, this would work so well if she was more "evil", like "I'll win you over no matter how much I'll have to scheme."
I like it when a story dealing with nobles (or other rulers) have political considerations involved. Erica would love to be sincere, but she's forced not to be. The scene where her father forbade her from apoligising to Harold is one of my favouries. I very much like how she needs to suffer emotionally because of it, as it brings her closer to Harold, whose life is, more or less, mental suffering. Otherwise Erica would be just a happy-go-lucky beloved noble daughter.
Harold and Erica's relationship is absolutely one of the things I love about this series.
-There was no "punishment" for a guy who betrayed his master and showed the truth to Erica because he was kind. Because as we all know, the power of friendship is strong enough to fight all consequences. Even a betrayal is no biggie in the picture.
Who would punish him? Harold doesn't know and the Sumeragi must appreciate him a lot for the betrayal. Of course those of us, the readers, who appreciate that scene are also thankful for what he did. He's a comedy character, but he's also one of the few people Harold could use to get things done because the Sumeragi were at his disposal. If Harold does learn the truth one day, maybe he will kick his ass. Hard to guess.