Oh, the fang and ying dynamic—so specific! For maximum impact, I'd lean hard into supernatural or monster romance genres. Think 'Twilight' fanfic but dialed up to eleven, where the fang isn't just a vampire trait but a central, dangerous allure. The kiss scene gains layers when the ying character has to navigate that literal sharp edge, a mix of fear and desire. Body horror-adjacent romance does this well, playing with the threat of injury as a form of intimacy.
For a completely different vibe, high-stakes action or thriller AUs work. Imagine a spy or assassin storyline where the fang is a weapon, and the kiss is a moment of surrender or truce. The tension isn't just romantic; it's survival. I read a 'James Bond' AU once where Q had retractable fangs, and the kiss with 007 was this incredibly charged, fragile thing. It wasn't pretty, but it was memorable.
Ultimately, any genre that treats the fang as an active narrative element rather than set dressing will make that kiss scene sing.