Do you want to see two increasingly attractive vampires flirt/fight/make-out (usually in that order) as plot allegedly happens in the background? Then have I got THE manga for YOU!
The story gets much better as it goes along (even though it still makes almost no sense unless you squint and editorialize the frick out of it and then eight chapters later realize what the point of it all was), and thankfully the series is short so that improvement is quick. The art also improves rapidly, to the point where Rayflo and Charles end the series as walking Greek statues rather than sort of generic yaoi figures. Problematic elements - like Rayfaelle's and Cheryl's relationship - are thankfully sidelined by and large, and the weird sexy maids' appearances are thankfully limited and even... used in interesting character development ways?
For all that basically nothing you learn in the first arc of this series has anything to do with the rest of the story and is presented in a truly confusing mess of plot and even highly contradictory to later story, it's oddly compelling. Okay Rayflo is just really attractive and him dancing around a purported tsundere for a relatively short manga jaunt was compelling, with some amount of making out but not making out. And when that's not enough for you, the potential for a pseudo soul redemption arc for Charles that you never actually get keeps you keeping back. Do you not understand where I'm going with this? Good! You've just experienced what it's like to read the first arc in this manga!
The rules in the worldbuilding for this manga make very little sense. At its base, some demon decided to I guess mock some version of the Bible by creating his own Adam and Eve, but as vampires. And they are different than other vampires because they are... older? Are they the first vampires? Mayyyybe...? Also the demon can't manifest on Earth so he made a copy of himself to stalk and repeatedly assault his not-Adam. But deep down he secretly cares about his babies so... he made a weaker baby for them to... start this race of super-vampires. Somehow. Also, the only vampire who isn't not-Adam and not-Eve is Charles and two vampires who get killed almost immediately after their introduction so... are Adam and Eve the strongest, or are they just like the only ones in existence? (it's very unclear whether or not Cheryl is a vampire or whether she will be one day) All the other 'vampires' are created by human science.
Charles is a cyborg. It's made clear only by the end of the story why he is a cyborg. Where did this technology come from? Are cyborgs common (doesn't seem so; and the story seems to take place in 'modern' day, not the future)? Is this a secret church science thing with highly advanced technology they keep secret in order to hunt vampires or something? Why doesn't the church use this to enhance other vampire hunters? Where ARE the other vampire hunters, and why aren't they going after Rayflo, Charles, and Rayfaelle? What is that not-ponytail cord he has on the back of his head for? If he has replacement vocal cords, why does he look like his whole jaw was replaced? If Charles and Rayflo both have wings, why do they not use them, and why do they need wings if particularly Rayflo can just turn into a swarm of bats?
Also, for all that Charles is purportedly a vampire hunter, he kills an entire zero vampires in the entire series (other than one by accident via distraction). Sure, you could make the argument that his work on Vassalord is to stop more vampire-like problems from happening, but the 'he's a badass vampire hunter' line kind of falls flat when the actual vampire hunting isn't what happens for most of the series (but hey, he depowers a demon clone! So... that's... well...). Also, Charles' abilities flip flop from being good at what he does to being pretty incompetent. In the opening of the story, he's shown to be quite powerful from a fighting perspective - but pretty much everything they come across is stronger than him. He's a Computer Dude cause Cyborg, so he's allegedly smart, but is defeated by a password not working. He's got superhuman healing abilities. He's a literal Cyborg. He literally falls from a plane in the air and walks away with a just a broken arm, while purportedly largely protecting two other people. He masterminds a Mission Impossible scenario to break Rayflo out of prison. But for whatever reason we're told that he would have had trouble breaking out of a human-filled gang-run area. Because...?
Also, why is Charles mostly immune to sunlight? This is NEVER explained. Sure, he's supposedly one of those rare ones, but given that we meet a grand total of four (and potentially five) 'real' vampires, including Charles, 'rare' doesn't mean what we think it means. A 1/4 or 1/5 chance is not 'rare'. We're never shown anything special about Charles to make this happen, nor is it apparently linked to his cybernetics. Since he's one of only two canonic second-gen vampires we meet, this is also unhelpful. He's Just That Speshul. Literally, this ability on its own is not a problem. But because of its lack of explanation, it just encourages this theme of "the rules don't matter and vampires get more powers because I said so." If it doesn't matter who has what powers, why should I care when new powers are introduced? Why do stakes - like story stakes, not stabby stakes - matter? Why do fights matter?
It's also never clear if real vampires are dead or not. I think they're supposed to be dead (because the primary benefit of the super-vampires introduced later is that they're alive). If they're dead, why does their blood revitalize other vampires? Why do vampires need to drink the blood of humans? I mean it never happens in the story anyway except like... once, supposedly, but if they're self-sustaining, why do they need humans? Admittedly Reyflo at least once has to drink some back-up blood to recover from one of Charles' feasts, so it's implied that humans have to come into the equation somehow, but it's very, very vague. Again, the rules of this universe are just nonsense at the best of times. And there's nothing truly wrong with these ideas themselves - that vampires gain powers from drinking the blood of other vampires. Other franchises do this. It's the way this story does it that's the issue.
I'm not even getting into Wayne's magic forensic capabilities or potential time-traveling prowess or how it's sort of implied that his agelessness is his only superpower for some reason but never canonically declared to actually be an ability because the pages for it are so vague. He wants to do a science thing? Well guess what, he can do a science thing because the story requires him to do the science thing. Him having vaguely amazing Science powers wouldn't be a problem if the story explained that this was his ability. He could just be magically really damn smart, or he's spent his immortality amassing scientific knowledge. But the story dances around it by just pulling out his abilities as the story requires. Give Charles his human arms and ears and vocal cords back? Sure! Create vampire-drugs? Sure! Fix the oldest vampire sort of? Sure! Genetic modification? Sure! Holodeck? Sure! (I'm not even kidding that this is a minor plot thread that's never explained for no reason but just dropped on us and then the characters literally walk away from it).
The primary relationship between RayfloxCharles is confusing at best and nonsensical at worst. It crosses a bunch of tropes as the story requires with a payoff that doesn't make sense from the viewpoint of the beginning of the story unless you take it from the getgo that Charles is just an idiot. At first it seems like Charles is a vampire against his will with a desire to murder his creator, but an inability to do so because killing Rayflo is nigh impossible, Charles has a modicum of self-preservation and oddly aligned but inefficient morality, which creates a love/hate relationship between the pair. But actually Charles has been in love with Rayflo since they first met. But also it was a sort of Father/son relationship so... eesh. Also Charles thinks of Rayflo as the Christian God and/or Jesus? But no, really, Charles is just a tsundere with really bad communication skills, and really, Rayflo is apparently really bad at communication, too. But no, Charles just wants to strangle Rayflo for groping him too much.
In short, it's just a really bad attempt to write a relationship where one party is a tsundere and the other is a wannabe playboy. Like at a glance it falls into a lot of typical yaoi primary romances, but it just bungles it so much with its kitchen sink formuale to developing the plot and character that it's just a mess of a thing.
The good news is that the last 1.5 chapters are pretty good rewards for getting through this whole mess of a story. I mean the characters are still doing nonsensical things, but hey, there's good humor and good payoff for the primary character relationship so and the art is pretty good (by which I mean DAMN there's some well-sculpted man-muscle in that bit of story). So... yay?
If you want some supernatural hijinks (ish) with attractive dudes sort of making out with each other every couple pages who also get progressively hotter closer to the end of the series, this is your cup of tea. If not, "Banana Fish" does a better mafia-centered shounen-ai story (and the anime has great art), that actually makes sense. "Doukyusei" is a cute shounen-ai story. "World's Greatest First Love" has a better overall plot with better humor (even if the art is terrible). "Natsume Yuujincho" is a far superior supernatural story. If you want good sword fighting, watch "Sword of the Stranger". If you want fun mixed-weapons combat, read/watch "Fullmetal Alchemist", or watch "Darker Than Black" or "Casshern Sins".