The NAP is also a natural law. It states that no person has the right to initiate force against another person.
It might be more precise, or at least clearer, to say that the NAP is a natural law because it state that "no person has the right to initiate force against another person"
while also having the right to not have force initiated against them in turn. In other words, if you do initiate force then others (the victim in particular) have the right to respond with a proportional punishment. Of course, this is what is generally meant by "one does not have the right to...", that one can legitimately be punished for doing so, but in this case it helps to make the symmetry explicit.
This is a natural law in the domain of logic, as opposed to physics. It is a natural law for the simple reason that if you can justify initiating force against someone else without provocation, they can use the same argument to justify initiating force against you, regardless of whether you're claiming that it is right to initiate force, or that it was wrong but you should be able to get away with it anyway, or that the rules are not necessarily universal... whatever argument you use can be turned back against you. No matter how you argue, the fact remains that you initiated force against a non-aggressor, and if you can justify it, so can they. If you
can't justify it, then you effectively admit that you deserve the punishment.