Hostile Killer points determine your Rank in Metin 2, Also they are for leveling up your Grand Skills to Perfect skills. (G-P) You can Gain HKP by either killing monsters your level or getting 1 Point per 3 mins. You can Lose HKP by killing your own Kingdom members or reading Soul Stones. While in Negative HKP you can lose some of your items when you die if you are over level 50.
You can have up to 20,000 Points and as low as -20,000 points.
The ranks are as followed;
Admirable = 12,000/20,000 Hostile Killer Points
Noble = 8,000/11,999 Hostile Killer Points
Righteous = 4,000/7,999 Hostile Killer Points
Worthy = 1,000/3,999 Hostile Killer Points
Civilian = 0/999 Hostile Killer Points
Villan = -1/-3,999 Hostile Killer Points (1 item will drop with a 20% chance)
Criminal = -4,000/-7,999 Hostile Killer Points (1 - 2 items will drop with a 30% chance)
Desperado = -8,000/-11,999 Hostile Killer Points (1 - 3 items will drop with a 50% chance)
Felon = -12,000/-20,000 Hostile Killer Points (1 - 7 items will drop with a 60% chance)
Please Note: Only characters over level50 will drop Items along with quest items when your have negative HKP. Gold on the other hand cannot be droped.