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.
Anvilicious: Sex slaves are bad. You are a sick, sick pervert for liking shows like this. You are a horrible person for liking girls beating each other up. And it gets worst from there. It makes Haze's moral look tame in comparison.
Moral Event Horizon: While the whole Platonic Hearts tournament involves lots of brutality, until the very end Aya tried hard to stay on the Good Side, with the whole fighting mindset taking its toll on her mind only in the later stages. But after she's backstabbed by her best friends and her love interest, giving her the nastiest form of The Reveal, she discovers that her parents may have fitted the Retired Monster bill, she sees her mother die in atonement and she's made aware that Cute Mute, Stepford Smiler Natsume's mom is the Mastermind behind her predicament, she simply goes to pay her a visit and kills her in cold blood.
It's only hinted since the screen fades to black, but it's so heavily hinted to leave no doubt.
It may be inferred that Aya simply ended what her mother started, thus trying hard to break the cycle by eradicating every one able to reignite it. But as circles are notorious hard to break, and it wasn't a good action to begin with, Aya may have crossed the Moral Event Horizon without a real reason, becoming as rotten as everyone thought she could end.
Something to consider is that Natsume's mother was stabbing pictures of Aya, and dolls of her when an unseen figure opens her door and she looks at the unseen person in horror. While it's heavily implied that Aya killed her, there's no evidence of the death of Natsume's mother, nor the fact that Aya is actually responsible if it happened. Natsume's mother may simply have been taken back into sex slavery by the Men In Black mooks because the office building destroyed by Aya's mother was only a "branch office."
But if she really did mean to terminate the cycle once and for all, then she's more of a Well-Intentioned Extremist than anything.
Of course, if she counts, Miko, Haruki and Natsume definitely do even moreso, given that they're the main architects of pretty much everything bad that happens in the series with only their own deaths and that of Natsume's mother being unintended.
Narm: Sure it's hopeful that the lady in red can bleed over 15 liters of blood from her head. Also the ending with Natsume's mother silent scream and black view, also known as the "Shallow Cheap Hentai Angst Ending" in the circles.
If you weren't down with this anime for the first four episodes then the infodumped thirty twist pileup in episode 5 will make it all worthwhile.
Nightmare Fuel: Seeing all of Aya's past opponents brain dead, completely mindless just doing stuff not knowing or caring why. The whole scene is pretty disturbing.
Also Aya killing Ryu and continually punching her dead body.
They Wasted a Perfectly Good Plot: While the show had some admittedly good ideas, the bad writing, animation, and the fact that it wanted to tell something big in just 5 episodes (the last episode being the big reveal) killed any chance of this OVA being any good. Also, its blatant attempt to have its cake and eat it too made said last episode fall flat on its face.