That's a fun little game. With loop player basically gets a smaller and smaller, until basically non-existing hitbox, making fighting him normally impossible. the way to surrender him though really works.
As already commented below, you have to stay by the wall (you basically almost don't have to move away from the throne at all), spam 3 and as he comes closer to you, avoiding the spell circle behind him, press 1 to make him go back into it. Funny enough, you don't even attack him yet, he just feels that 1 was pressed and reacts, lmao.
Like how there are little variations to the dialogue depending on what would you choose.
And I wonder how weak was the army if he only learnt how to slash with the sword by the first arrival to the Queen.