I tried to tell in survey about pvp/pk system i had in other game but i got limited space so couldnt that i will try to explain it here.
Everyone have white nicknames. If someone hit other player then he get purple nick (marked as pvp) if hitted person hit answer with hit then he get purple nick too. If u kill person who has purple nick then its all fine , no long term punishment. If u kill white person then u turn red nick (pk player). Killing a red nick player when he not fight back will not give red nick but only purple nick. Red nick player will drop more loot than normal players. To lose red nick u need to kill some amount of monsters , to lose purple nick u need to wait some time outside of any combat. Including our already implemented full inventory drop, i would suggest pk players to drop some of their equipped items on death too. Every time u PK a player and get red nick u get counting on your pk number. More PK count u have , more chances to drop items from you and more monster u need to kill to lose your red nick back to white.
There need to be npc that will lower your pk count by some amount for gold/quest/resources so ppl could keep pk others without spending long time of losing pk status (red nick) after like 10th or 27th pk.
Its best pvp/pk system i found in games over nearly 20years of my gaming activity.