In my universe, the source of Terra’s vampire legends are a species called Keratians. Their home is Toros, a large world that orbits a bright red dwarf. The gravity there is relatively intense. We would weigh five times greater were we to step onto Toros. That may not seem like much, but consider that on Uranus, you would weigh a little over eight times what you do now.
Keratians are humanoids and can easily be modified to appear human, provided they are not examined too closely. Their morphology is anything but, however. True to vampire lore, they do have a liquid diet.