With the reveal of Krul and Asuramaru being siblings, it certainly explains Krul's use of Double Entendre around Mika - it runs in the family.
In Greek mythology, redheads were supposed to turn into vampires when they died. What color is Crowley's hair?
Lest Kerr has a Greek name and is a redhead. Double brilliance.
Shinoa's weapon is a scythe. Seems mundane at first until you realize she's the daughter of the Hiragi family which owns the Moon Demon Company. Her Scythe is shaped like a moon!
Asuramaru is a figure of immense power in Hinduism. A fitting name for someone who can take down Ferid in 3 seconds.
Krul the first (relevant) character to appear onscreen. She's also the highest ranked in the Progenitor's council. The Fridge Brilliance? She appears first in both worlds! For the (human) viewers, she is the first character we see and for her (vampire) viewers, she's first in command.
Why was Guren so conveniently standing in front of the place where Yu escaped to? Of course he'd be there, he was conspiring with Ferid.
Crowley loves cars. His last name is EUSFORD.
A bit obvious one but how did no one notice Krul rescued the Hyakuya orphans and kept them safe? Well, who would bother going to the icky yucky poo-poo livestock place to check?
Why does Guren send Shinoa as Yu's supervisor? He sees Yu and Shinoa as the second coming of him and Mahiru!
'Lacus' is Latin for lake, 'Welt' is German for 'world'. His name means 'Lake World' - contrast it to his hair color.
On odd numbered manga covers, humans appear, on even numbered ones, vampires appear. Guren appeared on the cover of Volume 8 - hinting he was in league with the vampires all along.
According to the manga, the world entered the apocalypse in December of 2012—the exact same time when the Mayans and many others predicted the world would end!
How were Yoichi, Shiho, and Yu able to wield Black Demons? Simple, they were all experimented on previously. It only makes sense for them to own such powerful gear.
In The Story of Vampire Mikaela LN, a Muslim calls Crowley 'Shaitan' (it means devil in Arabic, and it's what Muslims call their version of Satan). The other crusaders point out it's because he's been killing more jihadists than anyone else, but it has another meaning when you take a look at his bright red hair.
There's a Russian saying: you can't pick your family but you can pick your friends. Which Russian character emphasizes on family?
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 was experimented on and that his remaining family (Yu) is exposed to the organization currently leading the experiment.
Chapter 46 reveals how Ferid kept Yu and Mika's deceased family's (Akane) decapitated head whom he killed presumably as a trophy and tells Yoichi not to take it out of its container or it will rot.
Also in the same chapter one wonders about Yu's mental state since basically losing his humanity and discovering a member of his beloved family had her head decapitated by Ferid after he killed her and has kept it since then. Also, if Yu becomes a complete demon imagine how Mika who cares greatly for Yu would feel. Vampires can only retain humanity so long as they have human connections after all. If for arguments sake, Mika had his way right now and the two of them managed to run away, he would be able to save his Yu and maintain whats left of his humanity for the time being, but at the same time, Yu wouldn't be able to retain his, knowing that he had betrayed and abandoned his comrades. Theyre pulling in the opposite directions, so first, they need to find a compromise. Luckily, Yu is charismatic enough to possess a potent power of persuasion, and Mika is sensible enough to be willing to believe in Yu and compromise, so they quickly found the common ground at the beginning of the chapter. But if, say, Yuu becomes a full demon, Mika might be be even worse off than Crowley, because not only would he lose his precious person, he would probably have to kill demon Yu with his own hands, and its obvious that it would destroy him mentally and emotionally.
Mika meets Ferid one night, missing out on dinner with his family and returning home after everyone except Yu has fallen asleep. He has blood on the right side of his neck when he returns. Ferid is revealed in the novels to bite Mika's neck in return for giving Mika anything from his mansion that he wanted. Biting turns out to give immoral pleasure to both the biter and the one being bitten. Therefore, their physical contact and Mika's tears and desperation to escape could very much imply that he likens it to being more like a sexual assault. This was severe enough for Mika to see escaping to the surface into a world he believed was completely devoid of human civilization and overrun by monsters as a preferable alternative. He also would do anything in his power to keep Yu and the others from being bitten and feeling the same helplessness and immoral pleasure to a futile extent as Ferid manages to bite Yu in chapter 46.