Byak-Ko was the ruler of World 3.
The world is essentially an island of solid clouds in the sky, with a palace and two towns.
Byak-Ko had ruled this world for quite some time. There was a resistance, originally led by Charles was the ruler of World 3. When Charles died, his two daughters, Jeanne and Mireille, took over leadership of the resistance.
Mireille was secretly working with Byak-Ko. The party learns this after rescuing Jeanne. After escaping the jail, the party confronts Byak-Ko. The fiend tries to kill Mireille, but Jeanne gets in the way. After the party kills Byak-Ko, Mireille's tears mix with Jeanne's blood to make the White Sphere.