In the first "Three Realms War", the Demon Emperor attempted to seize the Earth's Spiritual Marrow, the lifeline of the human world, in order to achieve his conspiracy to rule "heaven, man, and demon". Halfway through the war, the martial arts practitioners in the human world were killed or injured, and the three brothers Zhong Yunfei fought to the death. Just when the spiritual marrow was in danger, the highest god in the heaven, Emperor Xuanqiong, abandoned his immortal body and used all his spiritual power to seal the Demon Emperor. At this time, the Earth's Spiritual Marrow fell to the human world and combined with the souls of the three brothers Zhong Yunfei to regenerate the immortal body. However, because the spiritual marrow is a combination of yin and yang, the third brother Hanyan became a girl, making a lot of jokes. After the war, the remnants of the demon clan did not retreat from the human world. Zhong Yunfei volunteered to take on the mission and go down to the world to eliminate demons. Zhong Yunfei worked together and wanted to use the sword to sweep away all the injustices in the world, but he encountered difficulties again and again, and found that the right and wrong were far from being as simple as they imagined. In the setbacks and trials, the personalities of the three gradually matured and their strength gradually grew. Faced with the rampant counterattack from the demon world, he was willing to sacrifice himself to achieve justice and became the eternal guardian of the human world.