Well this is a Dark Fantasy series after all...
- The title of the series refers to the Seraphim, as in the highest-ranking angels in Heaven, ushering in the apocalypse because they hate all of humanity. They're Eldritch Abomination parasites with Old Testament powers who can only be stopped by demons. That's right, angels are Nazis and they ended the world, while the powers of darkness desperately tried to save the world to preserve their food sources.
- Straight off the bat, the adults dying all around Japan due to the virus and watching an 8-year-old Yu and Mika (who are the oldest) run to the orphanage with some of the Hyakuya orphans at night is just downright scary. Yu even watches someone die right in front of him before continuing on.
- The fact that some of the vampires have no problem stepping or walking right over children while they're coloring can be unnerving.
- And then there's Yu and Mika watching Ferid Bathory brutally kill off their younger family members one by one as they attempted to escape. Keep in mind that our young protagonists here are only 12 years old and could do little to nothing but watch.
- In the manga, Ferid casually decapitates one of the orphans.
- Mika takes the gun out of Yu's hand, only to be stabbed right through the stomach and then have his arm cut off.
- There's something disconcerting about Ferid wanting to see the orphans' faces twisted with despair and hear their screams as he's slaughtering them as well as the light novel depicting him drawing a map that he wanted Mika to find to help with their escape attempt to give them false hope.
- Ferid casually states that his massacre of the Hyakuya orphans was fun. It's not, but he saw the group of small children as potential psychopathic eldritch killing machines, and as a psychopath himself, took the threats out. The worst part? He was 5% right.
- There are a few rape attempts in the series. In the novels, Guren's demon tries to get him to rape and kill Mito, the Thousand Night soldiers attempt to rape Shigure and Sayuri, and in the Mikaela light novels, Yu and Mika come across a group of boys who are in the middle of attempting to rape a girl.
- The demon army keep poison tablets in their mouths at all times that they have to chew if they are about to be tortured, killed, used for information, kidnapped, or even raped. When Shigure and Sayuri try to avoid the rape attempts by ingesting the poison tablets Saito uses his chains to grab the poison tablets from their mouths. Luckily Guren shows up in time to save them. How he rescues them is no less terrifying though.
- Not to mention the undertones of Mikaela, Yu, and Kimizuki getting their blood sucked by Ferid.
- Numerous vampires drink enough blood from people that it kills them with them showing Lack of Empathy.
- A lady is affected by the demon's curse and willingly uses herself as a test subject by injecting herself with Guren's infected demon blood. Her hand turns into a monster leading Guren to have to cut it off and destroy it. Instead of being upset that she lost an arm the lady is unaffected and is merely happy she could help Guren with the research, considering it a necessary loss in the name of science.
- Chapter 51 and 52 has a couple pages where we see Ferid getting subjected to sunlight torture which is him technically being burned alive, and Krul is suffering the same treatment as well. Even if Ferid does deserve it for his atrocities in the past...yikes.
- The fact that Mika has been with vampires for four years all alone, with the same vampire who killed his family in front of him, AND with an undeniable thirst for blood shows just how sad his circumstances are. Not to mention learning that his entire family were experimented on and that his remaining family (Yu) is exposed to the organization currently leading the experiment.
- Chapter 85 reveals that the First Progenitor Sika Madu had created dozens of clones of Yuu and wouldn’t care if one or two were destroyed as seen when—hundreds of years ago—Noya casually killed one for discovering his, Ashera’s, and Krul’s secret meeting. Keep in mind that that clone was an innocent, very young child. Not only that, but according to Noya, the current Yuu is the first “adult” Yuu to have survived. Even if the current Yuu is actually the original Yuu, if Yuu found out that many clones of him had been made and murdered...
