Although Vincent is interested in the knife, he wasn't too inclined to enhance it since it doesn't seem to be too practical.
He also wouldn't use torture since he has a few Subordination Impulse Potions in his hands... This is actually just a charm-type potion and should only be a low grade or even a poor grade at that. It should only have a weak charming ability to the first person they see after drinking the potion.
However, after enhancements and ascension from his System, it had become a strong slave-making potion. There was no need to use such an evil Knife. As long as they keep drinking this potion before the time limit ends, theoretically, they can be kept forever.
Perhaps, he would only use the Omni Knife if he really hated this person and he wanted him to experience hell. Cutting them and then healing them afterward to make them feel endless pain could certainly be considered hell.
If he comes to hate a person, this knife may not even be enough.
