In the anime and manga series "Fist of the North Star" (Hokuto no Ken), Raoh kills Ryūken as part of his quest for power and his belief in the survival of the fittest. Ryūken is the master of the Hokuto Shinken martial art and Raoh's mentor, but their philosophies clash significantly.
Raoh seeks to establish his dominance and rule over others through strength, while Ryūken embodies the ideals of honor and the protection of the weak. Raoh believes that in order to achieve his vision for a new world, he must eliminate those who oppose him, including Ryūken, who symbolizes a belief system that contradicts his own. This act is also a pivotal moment that showcases Raoh's transformation into a brutal and ruthless warlord, setting the stage for his character's development and the conflicts that arise throughout the series.