So I really wanted the actual fic to be a perfect double drabble, which means this note is now longer than the fic, ahaha. I guess this also qualifies as "fic that could have been a meta" (in the manner of "meeting that could have been an email" but hopefully a more fun version than that!).
Textual sources for vampire!Fei Du's very plausible thrall abilities from eyes and voice:
“Fei Du generally didn’t speak at all loudly, and everything he said seemed to be ordinary human speech. But passing through his mouth, human speech could at once turn into something with a covert feeling of intimacy. It often led people to form one-sided affections. Though fortunately he usually spoke and then left, leaving others ample time to destroy their own illusions.” (ch. 4)
“Fei Du’s eyes weren’t entirely black. Their color was a little light and looked especially multifaceted in the dimness. When he looked fixedly at someone, his eyes always seemed to be speaking, making the other person sink into them in spite of themselves.”
(ch. 5)
“Fei Du looked up. The gaze hidden behind his lenses inexplicably made the investigator feel uncomfortable. For a moment, he even thought there was something demonic about the color of Fei Du’s irises. He couldn’t even tell whether Fei Du had just been asking casually, or whether he was a suspicious individual sounding him out.” (ch. 163)
And not specifically about the thrall, but on how unusual his eyes look in general:
“Saying so, he pressed a little closer to Luo Wenzhou, his eyes giving off varied light, radiating from the irises, distinctly spreading out, like a freeze-frame of ripples.” (ch 54)
“Fei Du undoubtedly had a beautiful pair of eyes, especially when he smiled, his irises refracting light in several layers. The gradations of a natural human eye couldn’t be replicated by even the highest grade of contact lens; it was a miracle of the accumulated accomplishments of hundreds of millions of years of slow evolution, containing the most complex and changeable moods and desires, the subtlest and most tortuous emotions, like a mustard seed in a fantasy novel, the whole world in a grain of sand. Evidently, Fei Du’s 'mustard seed' had an indestructible outer shell.”(ch 77)
“Fei Du met his gaze, two inverted images reflected in his eyes, as if they had encircled Luo Wenzhou entirely, refracting layer after layer of light, unbelievably dazzling.” (ch 96)
