Kumiko the Demon Girl

""Hi, there! I'm here to kill you!""

Ken Iwakami, college student, hopeless in love, and general slacker awakes to these words and finds that Kumiko, a succubus, has chosen his soul to devour. In desperation, he claims he doesn't want to die a virgin and she agrees to his request. Shortly afterward, she finds that she kind of likes this "sex" thing, and the process thereof has allowed her to eat a small amount of his soul. Thus, she decides to make him her property, complete with marking him and attaching a magical leash to his neck that keeps him from getting more than ten feet away from her. Add in an angel with a history with Kumiko, a long-dead ancestor of Ken, an insanely jealous judo girl, and a Nazi physics professor, and wacky hijinx ensue.

The original website disappeared years ago, but the first several chapters can be found on Fiction Press and The Vanished FanFic Archive has a copy scraped from an Internet Archive copy of the site. The comic strip adaptation done by the author has sadly been lost to the aether.

This show provides examples of:
 * Boy Meets Ghoul: There's Kumiko herself, and then there's his dead cousin who's returned as a Ghostgirl to make him fulfill his promise to her.
 * Horny Devils: All demons have bat wings and horns. The concept of a succubus is an invention by sexually frustrated monks though. They really just eat your soul.
 * However, Kumiko decides on a whim to indulge Ken's last request and finds that she is a Horny Devil for him.
 * Our Angels Are Different: They're and have very human emotions.
 * Supernaturally Delicious and Nutritious: This is Kumiko's excuse for why she doesn't eat Ken's soul all at once, a transparent excuse for hanging around to enjoy sex with him.
 * Tsundere: Ken winds up with two of these after him, a judoka and a biker girl, both of whom are convinced that Ken is the only person who can see past their tough exteriors.
 * Those Wacky Nazis: It's rumored that Dr. Josef Strauss was one of these..