Kougaiji is a youkai prince and the son of Gyumaoh, the Ox King, and Ratsetsunyo. He lives in Houtou Castle in India and is compelled to serve his stepmother, Gyokumen Koushu, whom he deeply resents. His mother has been cursed and turned to stone, and the promise of her revival drives him to pursue the Maten scripture and the other sacred sutras held by Genjo Sanzo and his companions. This mission places him in direct opposition to the Sanzo party, framing him as a recurring antagonist whose actions are born not of malice but of desperate filial devotion.

Despite his role as an adversary, Kougaiji possesses a fundamentally kind and honorable disposition. He is strong-willed, compassionate, and widely recognized as having a generous spirit. His loyalty to his mother is matched by a genuine warmth toward those he considers family. He is deeply protective of his spirited half-sister Lirin and maintains a close, brotherly bond with his bodyguard Dokugakuji, who in turn sees Kougaiji as a source of renewed purpose. He also inspires fierce dedication in Yaone, an alchemist he once saved from a deadly demon, and she remains steadfastly loyal to him. These relationships reveal a leader who earns trust through empathy rather than fear.

His rivalry with Son Goku is a central thread. What begins as forced opposition gradually reveals a mutual recognition of strength and struggle. In a pivotal and brutal death match with Goku, Kougaiji sustains critical injuries and is subsequently placed in the care of the calculating scientist Nii Jianyi. Under this influence, he is brainwashed into a merciless, single-minded killer stripped of his former warmth. This dark transformation illustrates how his intense love for his mother and his willingness to sacrifice himself make him vulnerable to exploitation. Over time, however, thanks to the steadfast efforts of his friends and his own inner resilience, he regains his true self and his moral compass.

Kougaiji is a seasoned and formidable fighter. He excels in martial arts and can project fire-based attacks with precision. His knowledge of youjutsu allows him to summon demonic entities, the most notorious being Engokuki, a demon of the flame prison. As a youkai of royal lineage, he possesses enhanced strength, speed, durability, and endurance. He has lived for over five centuries but retains the appearance of a young man. His regal bearing, coupled with the persistent conflict between his gentle nature and the harsh demands placed upon him, makes him a complex presence whose story blurs the boundary between antagonist and tragic figure.