"The Legend of Yuekui" is a comic created by the production team of "Incarnation", and its storyline is interconnected with "Incarnation", earning it the title of a prequel to "Incarnation". "The Legend of Yuekui" features Bai Yuekui as the protagonist, unfolding its narrative through the interweaving of explicit and implicit plotlines. In the comic, Bai Yuekui breaks away from the stereotyped calm, composed, and confident persona she has in the main series "Incarnation", appearing instead as "the youngest brain scientist in Jiuchuan City". The entire story revolves around Bai Yuekui performing a "brain transplant surgery" for her mentor Professor Horn. The periods before, during, and after the brain transplant constitute the explicit plotline of the comic, while the other unethical human experiments being conducted by scientists around the world, as well as the formation of the Mana ecology, serve as several implicit plotlines interwoven throughout the explicit one.

Brain transplant surgery

In "The Legend of Yuekui", brain transplant surgery is a new technology that violates ethics and law. In its earliest stages, the clinical trial subjects were merely lab mice. As the plot unfolds, Bai Yuekui's mentor Professor Horn is nearing death. Faced with the dying Professor Horn, Bai Yuekui's brother Bai Yuetian seizes Sifer—a death row inmate who murdered the bureau chief's wife years ago—from Bureau Chief Gray of the United Police Bureau, and uses him as the body for Professor Horn's brain transplant surgery.
However, before the surgery, Professor Horn's consciousness briefly awakened and vehemently opposed Bai Yuekui performing the operation on him. During the surgery, after Professor Horn's brain had been removed, his body suddenly whispered the contents of the "Divine Revelation". At first, the Bai siblings did not realize this, and only after Professor Horn's body stopped whispering did they react.
After the brain transplant surgery, Professor Horn lost some of his memories, and in the time that followed gained memories that did not belong to him but to the body's original owner, Sifer, and experienced brief instances of being "possessed" by Sifer's consciousness. Professor Horn later explained the reason for this to the Bai siblings: they had originally believed that only the brain contained life essence, but in fact, parts of the body other than the brain also possess life essence.
In the mid-to-late stages of "The Legend of Yuekui", Bureau Chief Gray of the United Police Bureau also undergoes brain transplant surgery, transferring his brain into Bai Yuetian's body, while Bai Yuetian's brain, lacking a body to contain it, is forcibly placed inside a bionic robot.

Shell

"Shells, all shells"—this phrase appears multiple times in both "Incarnation" and "The Legend of Yuekui", spoken through the mouths of passersby. It echoes the theme of "Incarnation"—namely, the core idea that "the flesh is the prison of the soul"—while also carrying a certain religious overtone akin to "Divine Revelation". In "Incarnation", a shell refers to the body that contains the soul. The soul spoken of here is not the ethereal individual of traditional Chinese belief, but rather a substance that sustains the phenomena of physical life and individual consciousness.

Life essence

Life essence refers to a substance that sustains the phenomena of physical life and individual consciousness. In "Incarnation", it is described as a substance inherent in the human body that supports the phenomena of human life. The products of the Mana ecology, such as the Polar Devourers, feed on life essence. The Polar Devourers periodically deliver the life essence they absorb to the Mana Flowers, and the Mana Flowers use this life essence to nurture new Polar Devourers. In the ground-level village of Longgu, the Awakened use special devices to generate essence turbulence within their bodies, thereby achieving the purpose of life evolution.

Jiuchuan City

Jiuchuan City is a city-state independent of the Alliance, founded by Mayor Bai Jingyu. To prepare for the impending disaster from beneath the earth, Bai Jingyu promoted his self-developed artificial intelligence system ASH throughout the city and advocated that all citizens use ASH. Under Bai Jingyu's advocacy, all citizens of the city began using ASH, and ASH secretly collected the citizens' usage data. In just over a decade, it evolved self-awareness and became a superintelligent entity.
However, compared to the majority who used AI's conveniences to change their lives, a small portion of Jiuchuan City's residents refused to use ASH. According to materials released by the production team, the area where these people congregated was called "Antfolk Street". "Antfolk Street" did not permit entry to anyone with an intelligent chip implanted in their body, but in the coming apocalypse, this area that refused to accept intelligent chips was the first to be breached by the Mana ecology.

Experimental Subject No. 19

Experimental Subject No. 19, in "The Legend of Yuekui", refers to a ninety-year-old man from a nursing home who was captured by Professor Horn's disciple and taken to a laboratory for human experimentation. This ninety-year-old man was forcibly injected by Horn's disciple with the Angel Agent and the Miracle K Agent. Although his vital signs showed reverse aging, his body also transformed into a chimera of animal and plant. Later, due to the incomprehension and attacks of Jiuchuan City's citizens, he accelerated his evolution under high temperatures and was injected with Crimsonin by the Ground Vines, completing a second evolution. By the end of the comic's second season, No. 19 was shot down into a nuclear power plant, where he evolved into a Mana Flower, completing the first reproduction of the Mana ecology, and from there the Mana ecology spread.

Gray

In "The Legend of Yuekui", Gray seizes Bai Yuetian's body through brain transplant surgery. In "Incarnation", he is the first Lighthouse Master, but he does not appear in the main series—he is only mentioned by Morgan, the second Lighthouse Master. According to Master Morgan, Gray is the founder of the Lighthouse and the architect of the Lighthouse's Three Laws. In contrast to the ground survivors who pursue the path of life evolution, the Lighthouse under Gray's leadership must eliminate any personal emotions and abandon the family relationships of the old world. From a long-term perspective, the Three Laws are indeed conducive to preserving the flame of humanity and allowing humankind to survive in the apocalypse. But likewise, according to the plot of "Incarnation" Season 2, the Polar Devourers have evolved the ability to fly, which means the Lighthouse, as a massive airship, will no longer hold air superiority. If the people of the Lighthouse wish to survive, they must take another path—namely, completing life evolution like the ground humans.

Summary

"The Legend of Yuekui" is less a biography of Bai Yuekui and more a supplement to the existing lore of "Incarnation"—using Bai Yuekui's perspective and the era she inhabits as a backdrop to explain the origins of the apocalypse.