@Tyth Vileblood That's because mc got the status window and holy emperor doesn't have it. And as a intelligent species vampires can hide their blood thirst as well as malice. So it is harder for even a seasoned holy knight to notice that.
@Idolist my brother he is the holy emperor the one that went on a crusade against the undead and you're telling me he can't figure out whether a person is a vampire
@Tyth Vileblood As they have explained in the previous chapters they take the bodies of their victims which makes them semi immune to holy magic as such even if he is the holy emperor he won't be able to sense there presence.