Story Related. Located in the Chapter 12 Conclusion.
This fight is annoying but not too hard. The giant has basically four moves. One he throws soldiers, gunners, and Pinocchios down to attack you, simply defeat them. Then he uses a catapult to shoot people/princesses at you. Keep moving and avoid the shadow cast by them. After this, he uses a dragon to reign fire down, just run from the flames. Fourth and last, he grabs you and uses a person/princess to kiss you with force hurting you. You can escape by moving the LS left and right.
To actually defeat the giant though, you need to wait for him to open the little door and punch him in his other eye. Do it to the point that he falls back and you are winning. Do it enough,and he will destroy his block castle and his father will take the remaining princesses away.
If you find this solution to be unhelpful, please tell me why in a comment and I will update it the next time I'm online.