These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
In John Polidori's short story The Vampyre, Ruthven is a sexual and psychological predator who befriendsAubrey and uses him as bait to draw in women. He murders Aubrey's Love Interest Ianthe, then fakes his own death, making Aubrey swear to tell no one of it. When Aubrey returns home, he finds Ruthven engaged to his sister, whom he plans to kill. Aubrey finally violates his oath, leading to his death; the warning comes too late, and the servants find Aubrey's sister the day after the wedding, drained of blood.
In Heinrich Marschner's opera Der Vampyr, Ruthven is a Satan worshipper, who must drink the blood of three women over a twenty-four hour period or forfeit his soul to Hell. He kills a girl named Janthe, then fakes his death after her father shoots him, making his friend Aubrey, who he once saved, keep his being a vampire a secret. The next day, Aubrey finds Ruthven has hypnotised his Love Interest Malwina's father into engaging them; he has also begun preying on a girl named Emmy. Ruthven kills Emmy, handing her soul over to his masters, then goes through with his plans to marry Malwina, while using his supposed friendship with Aubrey and the oath that the latter swore, to keep him from warning her and her father that Ruthven will kill her. In the end Ruthven is struck down by his own masters, moments before he can kill not only Malwina, but Aubrey too, whom he regards as a traitor for trying to stop Ruthven from killing his girlfriend.