Tera, a human character from the previous season of CASTLEVANIA: NOCTURNE, can be briefly seen in vampire mode in the trailer for season 2. The pointed ears are a big giveaway:
https://www.youtube.com/watch?v=tQt-irbJtq8&t=2s
I know it's unlikely, but I really,
really hope we'll get to see Tera's vampiric transformation in explicit detail, "American Werewolf in London"-style. (Skin complexion turning pale, ears growing pointed, fangs sprouting, etc.).
If not...well, that's what fanart is for, isn't it?
