I think you will end up just with the actual system trying to balance your idea. Is good, but maybe only for a certain area so ive developed this idea:
It could be cool that a place like a "Soul Valley" that is so corrupted by the power of the Gods Souls and the Humanity Influences that no one can be sure what is even happening. You can find three cool items:
-Black Sword Pendant: Used to invade other players. You adquire Black tendency by
killing the host, not just invading. You will appear as a colorless phantom.
-White Shield Pendant: Used to help other players, acts like a soapstone but you can also "invade" others world if they have some kind of beacon item. You will appear as a colorless phantom. You will get white tendency if you succeed helping the host.
-Grey Hand pendant: A pendant shaped like a hand. Used to invade other worlds. You will appear as a grey-ish phantom, with a cool aura effect.
-Soul Cipher: A relic from the old days. Its used to calibrate the aura effects in the fabric of reality. You can see your tendency meter with this item and also see if other worlds are touching yours.
Mechanics:-Color in phantoms: As we know, red=bad white=good yellow=better blue=ohgod/bad. In this area, theres no noob thing such as colors,
. Here, you use the soul cipher to know your tendency status, which goes darker or lighter as you kill hosts or help people.
-Tendencies in gameplay: You can use the black sword pendant even if your tendency is good and also try helping people ifyour tendency is black, but you
will be restricted to your tendency.
If your tendency is black, you will appear as a black phantom if you invade or try to help and you could be able to attack the host, even if he summons you to help him. Of course, you can help him and get some good karma, but he could attack you...
If your tendency is white, you will appear as a white phantom even if you are invading other players, and you will only be able to attack them if the host harms you. If you kill the host you will receive black karma. However, the more white karma, the more rewards you will have, giving players a reason to help other than genuine mercy. The rewards will only be unlocked after reaching the max white tendency.
-Grey Disciples: The executors. This guys use the covenant restricted grey hand pendant to invade people who are being invaded or summoning someone to help them. You will appear as a grey phantom, your tendency doesnt matter here. You will only be able to engage phantoms in combat. The hosts cant harm you. Reaching the top of this covenant will get you a restricted spell to suck karma off the hosts, balancing them and setting your karma darker or lighter depending on the type of karma you suck.
You will only be able to invade properly as a grey disciple if you have reached both max white tendency and black tendency.
Hope this kind of idea helped you.