The rules of Nanika, not necessarily Alluka, have to do with the methods by which someone is able to make a wish. There are quite a few of them that are involved with her ability, so here’s the full list of the currently known ones: Alluka has to know the person’s name before she can start giving them requests. There are difficulty levels to the requests that Nanika requires of the person before they are able to have their wishes granted. The difficulty goes up with each successful wish but is reset after someone dies from not completing the requests. If there is a person who dies in the middle of fulfilling her requests (but not from the request itself), someone else will also die, if not more than that. Each person can only make one wish at a time, which does not allow for asking for more wishes unless they are Killua, who is the exception to this rule. If a person disappears for whatever reason in the middle of making her requests, Nanika will not be able to make requests or basically grant the wishes of someone else until it is completed. A person has only one wish at a time, but they can add several layers to it to ensure that they get more out of it. In order to heal someone, Alluka must be able to touch that person. Killua is immune to most of these rules, including waiting until someone else is done with their wish and the wished number limit. All he has to do is issue a certain secret command to Alluka.