Byak-ko is encountered when the heroes try to save a girl named Mileille on behalf of her sister, Jeanne, only for it to be revealed that she had been working with him all along into ambushing the heroes. However, instead of killing the heroes outright Byak-Ko opts for imprisoning them instead, feeling the protagonists were of no threat to him. The heroes easily break free of the prison and use a flying machine to pursue him: catching up with him just as he gloats over obtaining the White Sphere, an important artifact needed in cementing his power over the third world. Byak-ko then attempts to kill Mileille as she was of no further use to him, but Jeanne leaps in to absorb the blow. The heroes then quickly battle the monster, but they are unable to kill him and the fiend decides to leave, thinking he had the White Sphere. However, it was revealed that the Sphere he had was actually a fake: the real Sphere only being obtained when Jeanne shed a dying tear. The heroes proceeded to use this sphere to progress further up the tower and entire the fourth world of the game.
- He was the only boss who was not killed by the protagonists after a battle