A typical bait and switch. The deranged mangaka tried to fool people in thinking this might actually be a creative yuri vampire story that doesn't revolve around a blonde vampire, but of course, people who hate dark-haired female characters are so sick in the head that they can't help themselves. The teacher is revealed not to be the actual vampire, it's the girl's classmate. Because why do something creative when you can write some boring, tiresome, maliciously intended trash depicting dark-haired female characters as victims and blonde ones as superhuman creatures as usual.