Nanami and Yuzuru wind up being a lot happier as vampires. The fact that Yuzuru's human life sucked justifies this on his part, and from what we (don't) see of Nanami's home life she had more than a bit of the Parental Abandonment thing going as well.
Seiji Hama as well. When Mina comments that the lifestyle of a captive suits him, he mentions offhandedly that it's better than some other places he's been held that regularly subjected him to torture.
Ivanovic, the most vicious and unhinged of the three Lords, leads a brutal attack on the Bund to capture Wilhelmina Vlad "Mina" Tepes for his own pleasure. Once there, he deliberately targets civilians, and has the innocent fangless vampires executed to draw Mina out of hiding. He also uses as shock troops werewolves he's tortured into feral beasts that have forgotten their own humanity. Ivanovic at points attempts to rape Mina when he can and has a disturbing taste for young girls, not caring that Mina is in her younger body as opposed to her adult form; he even declares he'll only enjoy her adult body after he's had his pleasure of the younger one. In the past, he was also Grigori Rasputin, and drove Russia into chaos and ruin. Mina barely rescued Grand Duchess Anastasia from being dragged to his bedchambers at the end.
Rozenmann, the most elegant, handsome, well dressed and polite of the three Lords, is also the most intelligent and manipulative. He tricks Ivanovic into invading the Bund, knowing the death and destruction that will result. Planning for his fellow Lord's death, Rozenmann set up Mina to be kidnapped and replaced by a doppelganger whose terrorist attacks he was secretly financing and patronizing. With Mina in his hands, Rozenmann has Akira (supposedly) killed solely to break Mina further, and injects her with a drug to freeze her in adult form to rape her later. While Ivanovic is a wild, furious warlord, Rozenmann manipulates nearly every bad thing to happen in the series, with nary a care as to the many innocent lives or mental trauma he leaves behind him in his quest of domination.
Gabe is a New York vampire crime boss sworn to Rozenmann who makes the most of his limited time. He is a pedophile and maker of child pornography who routinely taunts a stripper about paying a visit to her daughter Susy, who can't be more than six. After he learns the stripper is sheltering the runaway Mina, Gabe violently murders her friend and storms her apartment, immediately noticing how Susy is prettier than he imagined and attempting to seize her before Mina stops him. Gabe uses Susy and her mother as hostages so Mina surrenders under promises they won't be harmed. While Rozenmann's honorable werewolf retainer Gerhard is willing to give the assurance, Gabe makes it clear he has zero intention of not coming back for Susy When Mina asks to feed, he comments he thought her child form was much hotter and if he can have Susy when Mina is done. This disgusts Mina, who later comments that his blood is as foul as his soul.
Radovan Elichenko in life was a Serbian war criminal who, during the Bosnian wars, led his soldiers into a village while the men were away and slaughtered the elderly and the children. The women suffered worse. Any woman in their teens or over where taken and subjected to endless rapes and tortures. To escape justice, Elichenko became a Cudoviste or monster in the Slavic tongue-a vampire. He then joined Lord Ivanovic and carried out "purges" of any leftover clans in Ivanovic's territory. After fleeing to the Bund and betraying Ivanovic to gain sanctuary, Elichenko was confronted by the father of one of his victims who had become a vampire to hunt Elichenko down. When presented with a picture of the girl he'd raped and tortured, Elichenko sneered he'd done "thousands of Bosniak sluts" and only remembered them by how they looked "down there" before mocking him about having probably slept with his daughter because "Muslim men love to control their women."
Memories of Sledgehammer side story: Friar Bolton, the leader of a secret order of vampire killers once employed by the Vatican, murdered his more reasonable superior to take over the group. When a journalist who knew the truth fled, Bolton had him viciously tortured and nearly murdered Reiko, the man's daughter, to make him talk before Inspector Seiji Hama saved her. When serving as aide to a Colombian politician, Bolton empowered cartels to commit crimes over the country and kidnap his own employer's daughter with no intention of returning her alive. When Seiji saved her as well, Bolton had him captured and tortured by the cartel with his limbs removed, his eye and ears gone and his skin flayed before he was recovered by the vampires and placed in the Artificial Beastman project to heal him. In the present, Bolton engineers a series of terrorist attacks with no regard for collateral damage and violently whips his best agent, his predecessor's daughter Clarissa, with intent to send her on a suicide mission to dispose of her. When he faces Hama, he finally attempts to murder the man himself, along with Reiko when she intervenes. When Clarissa fatally poisons him, Bolton uses the last moments of his life to rant about how only he has the vision to see the extermination of all who stand against his ideals and how her father was too weak to see it.
Crazy Awesome: The Earth Clan Elders. If their outrageous stories are to be believed (and it's implied by a few characters that they are), they wouldn't have been able to pull any of their stunts if they weren't batshit insane. For instance, only these guys would consider killing a shark that ate them by eating it from the inside out.
Ear Worm: The Opening Theme, Aiko Nakano's "Friends". And the Ending Theme as well, Hibiku's "Tsumeato" — for some even more than the Opening.
Fetish Retardant: Mina's constant nudity can get pretty annoying instead of arousing.
How some werewolves are born. Only male children can be werewolves but even then there's only a thirty percent of the child being a werewolf. The only way to be absolutely certain of getting a werewolf is to have sex... with the man in werewolf form. As of the final chapters of the manga, there may be an exception to the rule as the female werewolves are making a comeback in the form of Sanin's older sister Tatiana.
That shapeshifting weapon had Akira on the ropes, running him ragged and keeping him guessing on whose friend or foe. Then managing to mortally wound him when it cornered him. All seems lost, right? Fortunately for Akira, the weapon tries to be sadistic and transforms into Mina to add insult to injury. This however has the effect of making Akira very angry that it would mock his love for her. He gains the strength to go wolf and bite the thing's head clean off.
The students who barricade themselves in a chapel only to open the door when someone they are largely convinced had been kidnapped several days ago by the vampires they were hiding fromasks to be let in. This is after Akira told them that vampires would play such tricks and Yuki reminding them when they were about to do it.
Sanin. First he was betrayed, brain-damaged, and nearly killed by the werewolf who was supposed to be his partner for life during their trial in Siberia with Akira and Angie. Then his half-dead body was found by Telomere, who forcibly injected him with chemicals designed to make him a psychotic killer. Then, Angie manages to get through to him and restore what little humanity he has left after, you know, the brain damage and chemicals... and a Manchurian Agent injects him with berserker serum again, forcing a traumatized Akira to put him down in self-defense. And of course, he's shown in flashbacks to generally be the nicest guy you could ever hope to meet. And to just twist the knife deeper, in a last remaining shreds of his sanity, puts Akira's gun under his own chin for him to do it. His final tear-filled words before Akira pulls the trigger? "I... I'm sorry... A-Akira...".
Akira himself. How about having to kill your friend when you were just a kid, then have to live with the feeling you're an animal, just to find out out that another friend who was presumed dead, shows up, and then you have to kill him.