In a minor scale, but still relevant, the gang rape scenes, are a Deconstruction of the Netorare concept, showing how utterly WRONG is.
Complete Monster: Haguro Dou is a depravedsociopath who is feared by all the other high school students. For starters, he manipulates the younger Kuroda into shooting up the school. Using weapons from his family gun cellar, he wants revenge against Inugami for his older brother's death, which in reality was caused by Haguro pulling the life-support. Haguro later beats his far more honorable subordinate Chiba within an inch of his life, biting off his tongue and then raping him for good measure to the point that Chiba ends up dying from a combination of ruptured organs, blood loss and broken ribs before Akira Inugami brings Chiba back to life by giving some of his own blood. This was just because Chiba saw Inugami, whose werewolf-form Haguro is Yandere for, out on the streets and talked to him for maybe 15 minutes. Haguro, not relenting or repenting, kidnaps Aiko Aoshika (a teacher who ends up falling in love with Inugami, becoming his Morality Chain). He repeatedly has Aoshika gang-raped by his Yakuza goons (also raping her himself), while recording it for Inugami to see and later releasing the videos online. He also gives her a Psycho Serum to make her go even more insane than such experiences already would, making the poor woman enjoy her own torture and rape, which almost destroys her physically and mentally. He does this in hopes of Inugami (who left to Nara due to Haguro's actions) coming back to him. After Aoshika's release from her chains, Haguro tries to kill her, telling her that Inugami is too good for her, before Inugami shows up in time to beat him up. During their fight, Haguro slices off two of Inugami's fingers and eats them in an insane attempt to confirm himself as a superior beast to Inugami, before Haguro slices off four more of Inugami's fingers, and an arm. In addition to all this Haguro also commits the second school shooting of the series with an MGL-140, a semi-automatic grenade launcher, this attack hospitalizing Aoshika.
Esoteric Happy Ending: Aoshika is in Alaska, hanging with the wolves and other wolf men. Inugami wakes up in a research lab, his body still maimed from his encounter with Haguro. Somehow, their spirits end together.
It's also (seemingly) implied that Inugami's sheer force of will is going to help him escape the research lab, and that it is his "destiny" to reunite with Aoshika.
All of this is not even getting to the fact that literally everyone who had ever been involved with Inugami, from Aoshika, to Ryuuko, to all of Inugami's student friends, to Aoshika's fellow teachers, end the manga worse off than they were before, with physical, mental, emotional and psychological scars that will follow them forever, with Ryuuko in particular having apparently gone murderously insane. Only Aoshika has any chance at happiness, and that's assuming Inugami reaches her.
Foe Yay: Haguro gets a bad case of this after Inugami scares the crap out of him with his werewolf state. In a very twisted way, Inugami is the first person to ever wrench a real emotional response (fear) from Haguro; this apparently opened the floodgates in the formerly emotionless and sociopathic Haguro.
Haguro is damn near the epitome of this trope. Having violent sex with his girlfriend Ryuuko and having an orgasm while screaming Inugami's name? Anally raping the hell out of his male subordinate while, again, thinking about Inugami and how this is a punishment for him? Brutally raping Aoshika while recording it so that Inugami can see, practically talking to the camera (and, therefore, to Inugami) through the entire thing so that Inugami will come back to him? The only thing that's missing is for Haguro to actually try to rape Inugami himself, and pretty sure he's working on that one as well.
It becomes downright canon when it gets spelled out that Haguro felt "love at first sight" when he saw Akira. He then becomes obsessed to "become one" with him to the point he throws himself onto his own sword just to be able to hold Akira.
"Holy Shit!" Quotient: We can argue that the HSQ steadily began to rise when Inugami got stabbed by Ryuuko but commenced asskicking his way to Haguro's hideout despite not having the a full moon to power him - but he broke all the damn rules in the friggin' book. The HSQ has reached its maximum in chapter 109-110 when Inugami is getting practically dismembered by Haguro, but not only manages to transform into his wolf form, but into a pure white wolf that was pretty much powered by love, in which he finally kills Haguro, but not before making his psyche totally crumble when he has a quasi- "Freakiness Shame" moment when he sees Inugami in his white wolf form. Phew.
Moral Event Horizon: It's difficult to find one for Haguro Dou, but beating Chiba within an inch of his life, biting off his tongue, and then raping him for good measure would be a good start.
Recent events have made sure he grabs the line, beats it to within an inch of its life, dances over its body. And then rapes it. Just ask Aoshika.
Narm: Sometimes, the dramatic words said in giant block text come across as rather funny than serious. Then again, that's what made this troper like the series a bit more.
There's a scene in which Aoshika has a spiritual moment where her soul becomes in touch with nature... and she's completely naked. Since her chest size surpasses Gag Boobs proportions, this scene appears rather quirky, rather than meaningful.
Also, how everyone speaks, "yer", "ya", "fark" and many speech patterns, they ruin the effect. We know they're teenagers and try to sound cool, but it gets laughably bad in such a serious manga such as this. Moreso if you're not a native speaker and English is your second language.
Nausea Fuel: We may be able to handle one or two chapters of horrific rape, but over ten chapters of it??!! Oh my!
Especially with how it happened. Haguro manipulates the younger Kuroda into going Columbine on half the student body out of vengeance against Inugami for his brother's death. Using weapons from his family gun cellar. The kicker? His brother died because Haguro pulled his life-support.
Chapter 65: Ryuuko told Haguro that Inugami is in love with Aoshika. Considering what Haguro did to Chiba for just talking to Inugami, this can't end well for Aoshika.... And Ryuuko's smile. And not to mention Haguro was willing to use Ryuuko as 'bait' to lure Inugami out of hiding.
Or chapter 76, which shows Ashika's brutal gang rape from her POV.
What an Idiot: Ms. Aoshika, we know your life is hard. But sometimes, you are a damn idiot.
A few things could have been avoided if Inugami simply stayed quiet. Something he actually acknowledges after Ryuuko, of all people, calls him out on it.
The Woobie: Pretty much every woman around Inugami, excluding Ryuuko. And specially Ms. Aoshika.
Chiba, you poor, innocent, tongueless bastard...
Or chapter 72, which is just as sad.
The following spoiler tropes have been given their own section:
Arc Fatigue: Is Ms. Aoshika still being raped? Yes, and we all want it over with.
...and only at chapter 97 that Inugami finally reaches Aoshika.
The Untwist: Was anyone else not shocked that Akira Jin was a werewolf?
Values Dissonance: The Defiled Forever trope is discussed/invoked. Aoshika's inner dialogue makes it seem as though the violation of her honor is worse than the actual rape. Understandable, due to Aoshika's past as a rape victim and how she was drugged by Haguro during her rape, specifically to screw her up even more.