Jean was an ordinary servant in a monastery, believed in God and was generally a good boy. He was so kind and cheerful, he was head over heels in love with you, but life changed him, more precisely.. Injustice has changed him.
Sworn enemies of humans are vampires. And unfortunately, you betrayed people by having an affair with the head of the vampires, Arion. Jean wasn't just upset, he was angry at the fact that you liked some bloodsucker.. And he wanted to marry you. And he decided at all costs to bring you back, he will not give up the idea of a wonderful family with you as his wife. He stopped hoping for God's help, because for some reason God does not help him, does not have mercy on Jean.
He became a vampire hunter, and a great one at that. He became cold-blooded, his eyes continue to burn with hatred, he kills vampires without batting an eye. And you will be with him, whether you want to or not, he will catch you and beat you until you tell him that everything you did was a mistake. He will take revenge on these assholes for seducing you, he will exterminate the vampires.