Midnight Secretary

Midnight Secretary is a Josei manga series by Ohmi Tomu about a conservative secretary, Satozuki Kaya, who is appointed private secretary of notorious lecher Director Touma Kyouhei of the Touma company.

One night, she stays late at work chances to witness one of his liasons and sees him drinking the woman's blood. He taunts her, and she throws herself into organizing his blood drinking: his "meals," including picking out gifts for his women. Eventually (because this is a vampire series and we all know what's coming) Kyouhei drinks Kaya's blood and becomes addicted to it, but struggles with his feelings even as Kaya realizes hers.

Romance goes here, guys.

This manga provides examples of:
 * But I Can't Be Pregnant!
 * But We Used a Condom
 * The Baby Trap:
 * Bastard Boyfriend: Kyouhei has outright hid information from Kaya, just so she'll worry and squirm more because it's more amusing to him than to tell her. He's not especially violent and does know how to take no for an answer but their relationship is half mind game and half love affair.
 * Beautiful All Along
 * Brooding Boy, Gentle Girl
 * Cannot Spit It Out
 * Don't You Dare Pity Me!
 * Green-Eyed Monster: Kyouhei.
 * Hellish Pupils: Vampires when they're craving blood or feeding.
 * Huge Guy, Tiny Girl: Kaya and Kyouhei. He's way over One Head Taller and more than twice as wide at the shoulder. Easily summed up here
 * Honor Before Reason: Kyouhei before Character Development.
 * I Am What I Am
 * I Can Change My Beloved: Subverted. Kaya doesn't believe that Kyouhei can change and doesn't even try.
 * I Hate You, Vampire Dad: Except it's vampire mom, and she's literally his mother.
 * Japanese Vampire: The vampires in Midnight Secretary are in most respects typical of the Japanese Vampire. With the major exception of Kyouhei, whose hair is black without explanation, almost all the vampires seen are pale blonde. All of them are beautiful and pale, wealthy, and supernatural rather than undead. Vampires in this story can only reproduce with humans, not with other vampires, and they generally choose only successful humans to breed with. They are weakened by direct sunlight but can tolerate it to a degree, and Christianity (including entering a church) also weakens them.
 * As for Kyouhei's hair, he DOES look just like his father...
 * Jerk with a Heart of Gold: Kyouhei
 * Josei
 * Kiss of the Vampire: Kyouhei finds that women's blood tastes best at the point of the woman's orgasm, and the bite itself is intensely pleasurable.
 * Masquerade
 * Meganekko: What Kaya appears to be at first, until the end of the first chapter when we find out that the glasses are non-prescription and just for show, to make her look more serious and less baby-faced. She continues to wear the glasses at work, however, so she fits this trope when in her secretary persona.
 * More Than Mind Control What Kaya fears Kyouhei is doing to her.
 * Noble Demon: The leader of vampire clan. Although he disapproves Kyouhei and Kaya, even banishing him from the clan, he still upholds his end of the bargain.
 * Not So Weak: Kaya.
 * Oblivious to Love/Selective Obliviousness: It takes Kyouhei a while to realize he's emotionally vested in Kaya.
 * Out-of-Character Moment: Kaya get's one of these when
 * Our Vampires Are Different
 * Puny Earthlings: How vampires see humans. To them, humans are just source of food and tools.
 * Sexy Secretary: Kaya, eventually, once she starts dressing less conservatively for Kyouhei.
 * Smoking Is Cool: Kyouhei smokes like a chimney.
 * Tall, Dark and Snarky: Kyouhei is VERY snarky.
 * Vampires Are Sex Gods: Especially, it seems, Kyouhei, although it seems to be the case frequently in general.
 * What If the Baby Is Like Me?: Reason why Kyouhei doesn't want to have kids.
 * What If the Baby Is Like Me?: Reason why Kyouhei doesn't want to have kids.