These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Though it could also be Fridge Brilliance. Besides, if Shizuka and Arata's mother were incognito for years, that means Liesel being a sleeper agent is not out of the question, and since it's implied she's been on Earth for awhile, she already has a marked advantage due to having already sussed out the terrain of the battlefield.
There's a subtle metagame hint if you notice that unlike the other schoolgirls, Riko reacts not to Chris, but Arata. This means little in-character - but due to the game revolving around Arata, it implies that Riko might be more important than expected.
Fetish Retardant: The first sex scene between Arata and Chris can come off as this. They're driven nearly insane with lust by a side effect they weren't aware of, and their bodies just basically go at it without being able to stop themselves.
Foe Yay: Shizuka and Angela do not get a long, they respect each other and well, the tension is there.
Fridge Brilliance: Chris spent most of her life trying to deny she was a girl thanks to her desire to become Emperor. In addition to the situation with Shizuka, Chris also becomes embarrassed like a boy would when she accidentally walks in on Nodoka and her classmates changing for gym; usually a girl would have no more reaction to the sight of girls in their bras and panties than a guy would have at the sight of boys in briefs or boxers. It's possible Chris might have tried so hard to think and act like a boy that she started getting some "boy desires".
Moe: Regardless of the seriousness of the story; being an Eroge it's still in there, all though not many would have expected it to come from Liesel.
Padding: The writers took a leaf out of Nasu's book; the fight scenes definitely don't use one word when seven will do.
The Scrappy: Angela does a lot to make herself easy to hate. You will want to break something after the first fight with her. While she generally gets rounded off later on, April takes her place.
What an Idiot: It's implied that only virgins are allowed to join the Waltz, since it's a competition for the prince's hand. There are numerous cases of princesses winning a spot and celebrating... by having sex. At least two girls explicitly had to drop out because they got pregnant. Booze was involved both times, mind.
Woolseyism: At one point when talking to Suzushiro as Iris, Arata/Chris use 'ore,' which is an absurd pronoun for someone like Iris to use. English can't do that. Instead, they change it to make it as though instead of slipping with what pronoun they're using, they accidentally refer to themselves in the plural with 'we.'