Mismanaged Defense of Her Man.
Buffy Summers was busy tiding up the apartment where she lived with her boyfriend, Spike; they'd just recently gotten out of the camp where just about all of the HSTs were held in a state of practical slave-labor to build some form of a "Mystical WMD", once the situation was resolved, they were released peaceably, well, as peaceably as possible, considering the nature of the camp, that is.
She was cleaning their bedroom, and it hit her for some reason she didn't understand, to look into a drawer in the nightstand. Her hair was in a bandanna, and she was wearing a t-shirt as well as some jeans, and her favorite boots. What she found horrified her to no end: some truly filthy magazines.
In a rage, the lady ripped them in half, and threw the remains into the trash can nearby, promising herself that she'd talk to her guy about his choice in reading material; then it hit her: he was and had long remained a vampire, and she knew how perverted their intimate lives could be! A smirk grew on the warrior-woman's face as she considered how she would move against this perversion on her guy's part; it involved something she'd "employed" when she'd "experimented" with her own sex... she loved the young woman she'd been with, and regularly they stayed in touch through various means of social media, but this wasn't the end of it; far from it, in fact. "Now where is that item?" Buffy wondered to herself, putting her index finger to her lips to think things through as she stood, back to the bed, thinking as the sunlight streamed into the room.
One side-effect of this "mystical WMD" was that her guy, previously known as "William the Bloody" and before that simply by his name as "William Pratt". could now again walk out in the sunlight, direct sunlight. That was a plus, and it gave her a set of very perverted ideas of how to correct her man's perverted ideas of entertainment... she'd have to completely dominate him, something close to what she'd done before, so that was hardly a challenge, but boy was it risky for her soul, and her timing would have to be perfect in this regard; but all she could see was the need to go in and rescue her guy, so she went for it!
The aforementioned "device" was something that mimicked a part of the male anatomy, and, she'd used it once before, on her ex-girlfriend, Satsu, with their mutual consent; this however had to have her act far scarier; she had to really treat him as if she literally *owned* him, and to be rough with him if she were to make her point to him that this interest he seemed to have is completely unsafe.
Buffy knew she had some time to calculate her moves before her "target" came home and she had to put her "game plan" into action; it was going to be difficult to be so abusive yet subtle enough to make sure he didn't head out so that she could save her guy, and then to return to a lifestyle of tender gentleness and righteousness on her part.
Buffy knew that she should inform her teacher, Giles, even having returned to a minor, he knew a lot of the preternatural, so she knew he knew more about what was going on- some of his statements hinted at reading material to counter this influence, and she vaguely remembered that the being influencing her boyfriend was likely referred to as "Asmodeus"; a monster known as "the demon of lust".
It made sense on some level, but Buffy never bothered to think it through to understand what was going on- in a memory flash she remembered Kendra Young, a previous friend of hers, who would've grasped what was going on, but Buffy was more "action gal", less "think things through gal"; and that's where she made her tremendous mistake in tactics...