PSA: Just because you are "trying to get an S" does NOT mean you deserve every kill
I've seen this more than once in game.
Kills don't mean everything when it comes to what ranking you get. Sure, getting 20 kills helps, but there are many more factors that go into a ranking. If I've got the kill pretty much secured, and you have done no damage to the target yet, do not dash in and take it from me. Let me get the satisfaction and gold. You can get your S ranking WITHOUT stealing my kills.
Please and thank you.