If you had the crown, couldn't you just tell the giants
to split up in pairs, then each person in a pair beats/slashes the other person in the pair to death. If any giants are left alive, repeat the process by forming pairs, until at most 1 giant is left alive. Then that giant commits suicide.
On the one hand, they have to obey the order, because to not do so would be to reject their very existence. But if they do obey the order, they would erase their own existence. So I wonder if that would work.