How do you defeat an organization 13 member in kingdom hearts 2

This is kind of tricky, and it stumped me for a long time. While you beat most bosses by damaging them until their HP is gone, the Organization members are different. Since they are Nobodies, they don't actually exist. The only way to beat them is to let them take down all of your HP, thus causing them to switch with you. Since you didn't have any health, they then die.