Velvet is driven very strongly by revenge. She was deeply wronged by someone she loved and trusted and now wants to murder him. There's also a lot of guilt and grief mixed in there. She's also a daemon and exudes something called malevolence, which is basically dark energy produced by lots of negative feelings. It's what turns humans into a daemons in her canon.

Karna is generally pretty pure and free of negative feelings, but he pings as divine, if she'd pick up on that. Also I guess he was murdered in kind of an unjust way by Arjuna that one time, but he's not mad about it so shrug.