There are two ways of beating Kokujo. First team up with Light and nature cards is a good
way to beat him. But I defeated Kokujo by my Darkness Deck which is the best way.

You should use a Nature/Light combo deck that contains: Elf-X, Re Bil, Seeker of Archery,
Aeris, Flight Elemental and Milieus, The Daystretcher. An Essence Elf is optional to help
bring out your Nature and Light spells early......

Good Luck!