by the way the giant sword might be used by Luffy and not by Kid just like in Sun Wukong as he found the giant and heavy magical rod at the moment he pick it up he found out that this rod can change his size at his command. you would ask why Oda used a sword and not a rod. it is simply because it would be too obvious and every one would guess it. Oda would just spin it in the it can change his size and shape. i think Luffy would try to use because of desperation as Kaido would try to annihilate the people of Wano when he realize that he cannot win against Luffy. Luffy would use it as a rod since Luffy might has no idea how to use a sword but he use a rod in his childhood.