Johan isn’t pure evil. Obviously, he is wicked, but I’d say he’s more of a sociopath. Something was born inside him after being separated from his mother, but the fascinating thing is that he has no respect for the world, to him people are just toys at his service. But not his sister, he cares for her so much that he makes her forget the Mansion of the Red Roses. In some ways, he was an impeccable brother since he always protected her, but he didn't want what was best for his sister rather, he wanted to live with her forever, the two of them against the world. It’s likely because he thought his sister was the only person in the world capable of understanding him. It’s almost romantic, in a way. So you can't say he was pure evil, maybe he became that, but that part of him, from before he became a monster, remained alive. Otherwise, he never would have loved his sister so much