The Destined One.
Princess Iron Fan, originally named Rakshasi, was from the Kingdom of Rakshasa (not Russia, but a nation composed of the Yaksha tribe). However, the Kingdom of Rakshasa was destroyed by Ling Mountain. The Supreme Lord Laozi took Rakshasi in as his disciple.
After this, the Supreme Lord Laozi ensured that the prince of the Rakshasa Kingdom could reincarnate according to his plan.
He also gave the Banana Leaf Fan to Rakshasi (hence she was called Princess Iron Fan), who later married the Bull Demon King. He then forced her to drink the water from the River of Mother and Child, and through his manipulations, Princess Iron Fan eventually gave birth to Red Boy, the reincarnation of the Yaksha prince.
At the same time, using the pretext of Sun Wukong kicking over the Eight Trigrams Furnace, he demoted the boy who guarded the furnace to be the local deity of Flame Mountain, in reality to collaborate with Princess Iron Fan and Red Boy.
Initially, the Bull Demon King had a good relationship with Princess Iron Fan and doted on Red Boy. However, Princess Iron Fan later confessed to him that Red Boy was not his biological son and that the Bull Demon King was merely used as a cover by the Supreme Lord Laozi (though the specific reason was unknown to him). This made the Bull Demon King very angry, and he left home, choosing not to interfere with Princess Iron Fan. Outside, he met the Jade-Faced Fox, and the two demons fell in love and had a daughter named Pingping.
Although the Bull Demon King rarely returned home, Red Boy and Pingping had a good relationship. Eventually, Red Boy also left home to establish his own domain, calling himself the Holy Infant King.
Red Boy
Red Boy wanted to eat Tang Sanzang's flesh, so he transformed into a child and cried for help, capturing Tang Sanzang and taking him to the Fiery Cloud Cave. Sun Wukong learned that Red Boy was the son of his sworn brother from 500 years ago, the Bull Demon King, and tried to use this relationship to ask for his master's release. Red Boy did not believe what Sun Wukong said and spewed smoke and fire from his mouth and nose, driving Sun Wukong and Zhu Bajie away.
The Dragon Kings were summoned to spray water on Red Boy, but Red Boy's fire was the True Samadhi Fire, which could not be extinguished by rainwater, and instead, Sun Wukong got covered in smoke and fire. Zhu Bajie went to ask Guanyin for help, but was tricked into the cave by Red Boy, who had disguised himself as Guanyin. Sun Wukong then transformed into the Bull Demon King but was caught in a flaw by Red Boy. He then flew straight to the South Sea on his somersault cloud and asked Guanyin to subdue Red Boy.
Flame Mountain
Tang Sanzang's journey was blocked by Flame Mountain, and Sun Wukong sought the Banana Leaf Fan: Tang Sanzang and his disciples passed by Flame Mountain, and they needed the Banana Leaf Fan to extinguish the 800-mile fire on the mountain to pass through. This fan was in the hands of Princess Iron Fan, the wife of the Bull Demon King. Prior to this, Sun Wukong had fought with Red Boy, the son of the Bull Demon King, and had asked Guanyin to subdue him; he also had a fierce battle with the Bull Demon King's brother, Ruyi True Immortal, which further deepened the enmity between them. As expected, when Sun Wukong went to borrow the fan, Princess Iron Fan, holding a grudge, refused and fanned him 50,000 miles away. Sun Wukong obtained a Wind-Fixing Pill from Lingji Bodhisattva, transformed into a small insect, and entered Princess Iron Fan's stomach, forcing her to hand over the fan. This was the first attempt, but the fan he obtained was a fake Banana Leaf Fan, which made the flames a hundred times stronger.
Sun Wukong then went to Jilei Mountain to find the Bull Demon King, who had married Princess Jade Face, to borrow the fan. The Bull Demon King was invited away to a banquet. Sun Wukong stole the Bull Demon King's mount, the Golden-Eyed Beast, and transformed into the Bull Demon King, tricking Princess Iron Fan into giving him the real fan. In his moment of triumph, he was careless and the fan was snatched back by Zhu Bajie, who had been transformed by the Bull Demon King.
Sun Wukong and the Bull Demon King fought fiercely, with Zhu Bajie, Sha Wujing, Nezha, and the heavenly gods joining the battle. In the end, they forced the Bull Demon King to reveal his true form. Sun Wukong used the Banana Leaf Fan to extinguish the mountain fire, and the four disciples continued their westward journey to obtain the scriptures.
After the battle at Flame Mountain, the Bull Demon King was defeated and converted to Buddhism.
Following Sun Wukong's death, the Bull Demon King was rewarded for his merits and returned to Flame Mountain. However, his temperament changed drastically; he declined all invitations and shut himself away, seemingly troubled by some unresolved issue.
Later, Guanyin also released Red Boy, and the family of four enjoyed a period of harmonious days.
Because the Bull Demon King had kept the Great Sage's essence hidden in his stomach and was burdened with accumulated worries, his appetite decreased, and he became increasingly emaciated, with his appearance showing signs of aging. It seemed as if he was weighed down by heavy concerns. Sometimes, he would even revert to his original form, retreat to the mountain peak, and lie on the hillside, dry heaving.
After learning about his origins, Red Boy clamored for revenge every day. Fearing that he would cause a disaster, the Bull Demon King locked Red Boy up and assigned the Water-Avoiding Golden-Eyed Beast to guard him. Unexpectedly, Red Boy managed to escape, and the Water-Avoiding Golden-Eyed Beast chased and bit him. Red Boy pretended to be injured by the beast, and in a moment of panic to save his son, the Bull Demon King injured the Water-Avoiding Golden-Eyed Beast.
With his mount driven away and his weapon, the Mixed Iron Rod, lost (in the game, after defeating the Crimson Gold Chariot, you find the large iron rod in the cave, which is the Mixed Iron Rod, and the memories on the rod take you back to the Biyu Cave many years ago), the Bull Demon King was helpless as he watched Red Boy wreak havoc.
Red Boy demanded that the Bull Demon King hand over the Great Sage's essence, but the Bull Demon King refused, even at the cost of his life. Consequently, Red Boy imprisoned the Bull Demon King, intending to disguise himself as Pingping to lure the little monkey and then trick him into revealing the Bull Demon King's Great Sage's essence.
Yakas are the mightiest of the eight legions after all.
Be your body hard as metal, meeting death in scores is inevitable.
Yet, why did you endure the fish and those carts just as poorly?
You rush like wind with a clouded mind. It's your desires that shape what you see.
Had your mind been less unsettled, would you still have fallen for that child's play?
Haste oft blinds, while patience illumines.
Next time, can you still fulfill as Wukong without Bajie?