In the pause menu, the green experience bar grows with each enemy you kill. With this glitch, you can fill your experience bar and the armor , weapon, and spirit bars by only killing one enemy.
First, kill an enemy. Next, make sure you only have 1 or 2 experience points in the green bar. Now, instead of putting the experience points in by pressing up, press X to split the points evenly between the three areas. Since 1 or 2 cannot be split evenly into 3, the game just puts 1 point in each column. Now, you can go to each area and take the points you just made appear and put them in the desired area(s). Repeat and enjoy.