He is a youkai prince residing in Houtou Castle with his father Gyumaoh and mother Ratsetsunyo.
Known for his strong will and kind heart, he excels in martial arts and can emit fire projectiles. He is also knowledgeable in youjutsu, including summoning spells like his famous Engokuki (Demon of the flame prison).
In Saiyuki, Kougaiji opposes Genjou Sanzou and his party, as he is coerced into working for his stepmother Gyokumen Koushou, whom he despises, to retrieve the five Sutras, including the Maten Sutra from Genjou Sanzou. His goal is to get Gyokumen Koushou to revive his mother, Ratsetsunyo, who has been cursed and turned to stone in Houtou Castle.
Kougaiji's devotion to his mother and his kind nature earn him unwavering loyalty from his followers and companions, including his half-sister Lirin, his personal bodyguard Dokugakuji, who acts more like an older brother, and his alchemist Yaone, whom he saved from the man-eating Hyakuganmaoh.
In the sixth volume of the manga, Kougaiji makes a near-fatal mistake by challenging Goku to a death match for the sutra. Both sustain severe injuries, with Goku removing his limiter and unleashing the unstoppable Seiten Tasei. Dokugakuji manages to bring the injured prince home but must hand him over to Nii Jianyi and his scientists for care. Kougaiji reappears in the eighth volume, now healthy but brainwashed. Nii reveals that Kougaiji's mind was holding back his conviction, weakening his power against Goku.
(Source: Saiyuki Wikia)
