Master Karl appears as the antagonist of the "Path to Victory!" episode. He is first seen in "Path to Victory!" during the prologue of the game, defeating Samantha Kino in a game of Victory Battle, and is the final opponent who goes up against Yuuji Kino in the Card Championship. During the battle, Karl warns Yuuji that he cannot win and if he wins, a huge calamity will happen and change Yuuji's life and the world. Master Karl is faced with his demons: Satan, Lucifer and Fenrir. When a demon is defeated, Master Karl will cast Samecarecarm to revive it, what makes Yuuji to target and attack him directly.
In the "Final Battle" episode, Master Karl appears as the leader of the Human Resistance and as the representative of the Normal (Neutral) alignment. He shows to Yuuji Kino that the Eastern District of Tokyo is destroyed and that several demons starts to bring chaos all over the World, and their source is in the Lost Caves, in the North District. Later he appears with the Resistance if Yuuji is NEUTRAL aligned, to bring peace to Tokyo. In the Savior (Law) and Demon Lord (Chaos) routes, he is killed by Yuri Takano, in order to prevent further rebellions.