This chain is feet long if im not incorrect as he pulls it upwards Mifune just turns his hand letting the link slide from the tip of the blade and cutting the link he had stabbed. This chain link is made of bone correct? Mifune's sword can cut through concrete with ease there shouldn't be a problem there. Also he wasn't stabbing feet into the ground it was more like he was holding the chain down and leaning on the sword not kneeling down with his sword stuck all the way through it. If he had been then trying to pull it would put Mifune in the point of leverage anyway and the bone would snap on the sword.