Well, there are a couple things that led me to think that--although I freely admit maybe I've just watched too much Tsukuyomi lately and am jumping to the wrong conclusion
- Matsuri talks about how she wishes it would rain, implying that somehow she can't stand a blue sky (or sunlight). She also mentions cutting through the park, and says "even if the rain stops, there's still eaves there". If she really can't stand daylight, she could be saying she could safely wait under the eaves for the sun to go down.
- Mayuko and Takeshi talk about looking for someone, and Mayuko has to hide for some reason, which makes me wonder if she's hiding from other people, or if Mayuko's also hiding from the sun. Mayuko says (about the person they're looking for, who may or may not be Matsuri) "do you think she's wandering around day and night sipping tomato juice out of a wine glass"...and if vampires can't get blood, sometimes in other anime they use tomato juice as a substitute.
- Mana and Koyori talk about someone who's 'maybe not human' at the old abandoned church. Takeshi also mentions how the person him and Mayuko are looking for couldn't possibly be hiding somewhere as convenient as an old abandoned church. Later, Matsuri says "tadaima" (I'm home) after opening a creaky-sounding door, and no one answers--which is exactly what I'd expect if she was coming 'home' to an old abandoned church she's hiding out in.
- Aono warns Yorito to be careful because it's night out--this might not mean anything, but if Aono were aware that vampires existed, that could be why. Aono gives me that "I know much more than I'm telling you" vibe for some reason...
I guess when I write it out, it's really not much proof that anyone's a vampire
--but there's definitely something interesting going on...after listening to the prologue I really can't wait to see this now