@Doomer
When you kill someone you get cursed. The more you kill the more the grudges build up. You can actually relieve this curse by asking for forgiveness from the church. A priest will alleviate it depending on how much you may regret it.
Normally, the feeling is only slightly. Like if you see a generic soldier who saw some action you may feel they look tough or if you see a famous General you'll feel taken aback. But in MC's case he killed a lot, in a short time. To the point you would even call him a Demon King.
If you are a law abiding citizen, you'd get those curses relieved, both buy time, penance, and the church. But for the real scumbags, it just grows. So you can basically tell a good person from a bad person by that aura along. With some exceptions.