Guren: Is he a tragic hero who risked a lot for the world or a selfish jerkass who believed the end justified the means?
Krul's true feelings about being a vampire bring up to question the average vampires' attitude. Are they actually proud of what they are and do really feel contempt towards humans in general, or is this just an attempt to hide the reality that they are nothing more but former humans that unwillingly became immortal beings with most of their emotions and humanity gone for good and are forced to drink blood for the rest of eternity?
Jose, Crowley's squire from the light novels. Is he really a cheerful, optimistic little boy who wishes to fight for Christianity in the Holy War, or is he a Stepford Smiler who lacks any sort of self-worth and thinks that becoming a Templar and killing Muslims is the only way he can earn respect? One of the lines from the light novels is "...coming from a family where honor didn't exist, he put everything on the line for Pride and Honor".
Awesome Art: Be it the anime, the manga or the manga for Guren's light novel, the art of this series is gorgeous.
This mostly happen between fans of Yuu/Shinoa vs. fans of Yuu/Mika, on both sides. Let's just leave it at that.
Generally averted for Krul, however. She is a well-liked character and it's easy to read her and Mika's relationship as a motherly one, so people who don't like Krul/Mika usually write her as Mika's mom or older sister in fanfics.
Krul. Not terribly much screentime, but loved for her design, the fact that she saved fan-favorite Mika and her mature personality. Her fans were enraged by what happens to her near the end of the Nagoya arc, and they're happy she recently gets more screentime as her past is revealed.
Shinya. He rarely appears in the first portion of the series and is mostly there to be part of Guren's storyline, but fans love him for being one of the most likable characters in the series.
Lacus Welt and René Simm. Although they are very minor characters, they're actually rather popular in fanfics, usually being Mika's friends.
The demons are very popular for their interesting designs, personalities and the vast theories on how they became demons and got sealed, how their human lives were and how they came to know Shikama Douji.
Fan-Preferred Couple: On the het side, Yuu/Shinoa, Yuu/Mitsuba, Shinoa/Mika, Guren/Mahiru, Guren/Mito and Mika/Krul. On the homo side, Guren/Shinya, Yuu/Mika, Yoichi/Shiho and Shinoa/Mitsuba are the top popular pairings.
Foe Yay: Ferid has a peculiar fixation of this nature on Yuu and Mika, Krul once kissed Mika to transfer blood to him turning him into a vampire, and Crowley comments once on Yuu being "cute".
Growing the Beard: It is generally agreed that the second cour marked a major turning point in the anime adaptation.
The two main tsunderes of the series, Mitsuba and Mito, happen to have both of their names starting with "Mit".
The anime has a lot of similarities with the Barney & FriendsCrack FicDay of the Barney Trilogy. The main premise is that all of the world's adults have been killed leaving the children behind, humanity being ruled by Really 700 Years Old beings, humans working together to overthrow said beings with the help of one of them and a post-apocalypse scenario.
Informed Wrongness: Yuu gets this with Kimizuki when he saves the latter from a vampire squad, and he gets lectured for not trusting his teammates enough when it was Yuu's presence that specifically saved Kimizuki from certain death.
Yuichiro "Yuu" Hyakuya, The Protagonist, was abused by his biological family due to his supernatural nature. Sent to the Hyakuya Orphanage, Yuu was tested and experimented for them yet he found happiness on his fellow orphans. Surviving the apocalypse and being captured for Vampires, Yuu is forced to a serf life and tries to escape, leading to the murder of his family at hands of Ferid Bathory. Escaping thanks to the sacrifice of Mikaela, Yuu joins the Japanese Imperial Demon Army and trains to be able to avenge his loved ones. During the series, Yuu's true nature, use of his Cursed Gear and traumatic experiences start to erode his humanity, turning him into a danger to others and himself. While managing to achieve small victories such as reunite with Mika, befriend the members of the Shinoa Squad and kill important vampires, Yuu's obsession with family and his loss of humanity remains a question to be answered, yet he continues moving fowards, moved for his own desire to have a family.
Mikaela "Mika" Hyakuya, the Deuteragonist, is Yuu's last surviving family. Abandoned by his family and used for the Hyakuya Sect, Mika also loses his fellow orphans in an attempt to escape from the vampires before sacrificing himself to ensure Yuu's escape. Turned into a vampire and forced to work with a species that he hated, Mika started to hate both humans and vampires while also avoiding to drink human blood, surviving with the blood of Krul Tepes and being forced to work alongside his family's murderer. Wishing to reunite with Yuu, Mika manages to escape from the vampires and reunite with him before running away from the Japanese Imperial Demon Army, eventually completing his Vampire transformation after drinking Yuu's blood with his permission. Initially unwilling to work with anyone but Yuu, Mika is forced to accept the help of the Shinoa Squad to protect Yuu and eventually even with his hated Ferid Bathory. Hating his own nature and wishing to become human again, Mika just wants to protect his last surviving family.
The King of Salt Explanation The moniker Yuu is given in the final episode of the anime's second season which quickly became a common way to express displeasure for the anime's ending.
Big Brother is watching Explanation Asuramaru turns out to be Krul's big brother, who watches everything through his eyes.
MY QUEEN!!/ALL HAIL THE QUEEN!!! Explanation As mentioned in Ensemble Dark Horse above, Krul scores very well with the fans and almost everyone loves her, so this tends to be the general reaction when she appears onscreen.
Owari no Suffering. Explanation This series has plenty of angst and almost every character has a tragic past.
Seraph of the Gay.Explanation The sheer amount of both Ho Yay and Les Yay has made lots of fans joke about it.
Who's Mitsuba? Explanation Mitsuba's lack of focus and development has many fans, especially on Tumblr, joke about it.
Memetic Molester: Ferid. The fact that he always look like he's going to rape someone doesn't help.
Mind Game Ship: Ferid takes great pleasure in screwing with people's emotions what with him being a sadistic vampire. In particular, he has a peculiar fixation with doing this to Yuu and Mika respectively. Not even his close pal Crowley is immune to his machinations.
More Popular Spin Off: The light novels are widely agreed to be of better quality than the main manga. The fact that Takaya Kagami is already an author helps immensely.
At the very end of the final episode, Yuu wades into the ocean, holds out a hand, and proclaims, 'it's raining'. It's a very silly scene in an otherwise calm but upbeat ending.
Krul's appearance for some. She's supposed to be the leader of a race that consists of evil bloodsucking monsters, but she looks like such an adorable little girl it's hard to see her as threatening. However, considering that she's later revealed to be a more sympathetic villain with a dark past and her true motivation is just to be with her brother again, it's possible that she was never meant to look intimidating in the first place.
The number of times characters preach about family and friendship can get somewhat cringe-worthy and ridiculous.
Nausea Fuel: The image of a smiling yet blank young Shinoa strapped to a chair by her arms and legs with the strong visual implication of all of her finger and toenails ripped out.Though as it turns out it was just a ruse played by her older brother to get both Mahiru and Guren to comply with his demands. Shinoa was even innocently in on it without really understanding what was really going on.
How some fans react to Krul/Mika, given that this pairing has heavy pedophilia undertones going both ways: On one hand, Mika is a 16-year-old teenager while Krul has the body of a 12 to 13 years old little girl; but on the other hand, Krul is a thousand years old woman while Mika is just a little boy comparing to her. And even though biologically, they are not that far apart in age, Krul has explicitly◊ called Mika her son once. Yeah, Krul herself doesn't see Mika that way.
Ferid/Mika or Yuu/Ferid is also this, in a several more disturbing level. His dialogues with them reek of pedophilic undertones, which is why lots of fans see him as a Memetic Molester.
Aside from Yuu's obliviousness to Shinoa's feelings for him, Yuu/Shinoa is a nice pairing in general... except for one big problem. Shikama Doji, Shinoa's demon, plans to take advantage of her feelings for Yuu to take over her body. Worst scenarios might have her ended up a demon just like her sister. Because of this, some fans decide not to ship Yuu/Shinoa... at least until the Shikama Doji problem is taken care of.
Despite them being the Official Couple of the series, the present Guren and Mahiru can come off like this as well. Not only due to Mahiru being a sociopathic demon, but also that she's the one who killed his entire squad, including Shinya.
For shipping reasons, some Yuu/Mika fans won't leave Shinoa alone. In turn, some Yuu/Shinoa fans won't leave Mika alone.
Guren slowly became this for some fans, further pushed after the reveal of him causing the apocalypse from resurrecting his friends, and is manipulating Yuu to bring them all back to life even when it could not only destroy him but the entire world for a second time.
Lacus in some fanfictions can be a downright jerk.
Crowley/Shinoa or 'Crownoa' has quite the following.
Despite their limited on-screen time being together, some fans have started to ship Rigr Stafford/Saitou with Urd Geales, due to them both being Second Progenitors and had a history together back when the First was still with them.
There's actually quite some Raimeiki/Gekkouin fanarts on tumblr, in spite of these two having never interact with each other, on-screen or not. It's probably because they are both sexy-looking demons.
Shipping demons with their owners is quite common, such as Yuu/Asuramaru, Yoichi/Gekkouin and Kimizuki/Kiseki-O. Although in the case of Yuu and Asuramaru, it's recently revealed that they knew each other a thousand years ago, back when Ashera was still a human, so it's less of a ship in the night than the others.
Win Back the Crowd: The series caught a fair number of people's attention due to its premise, but the slow pacing of the first cour of the anime's run did hurt interest. However, the second cour has received much more positive reception between better pacing and character development.
Many fans have expressed frustrations that out of all the members in the Shinoa squad, Mitsuba gets the least lines, plot-related character development, plot significance, and screentime. She doesn't even have a proper, fleshed out backstory and motivation, unlike Shiho and Yoichi. It seems her only role is to balance out the gender inequality ratio of the Squad.
Crowley's comrades from The Story of Vampire Mikaela. They seem like the coolest guys ever who you'd want to be friends with, especially Gustavo and Victor, but they only seem to stick around for five pages of the light novel before getting killed off.