Gui Mu is the Great God of the Plague Affiliation.
Gui Mu's appearance is that of a tall and wiry great god with gaunt, prominent features. His wrinkled skin and deep-set eyes are of a strange pale blue shade. In his first appearance his hair was black, but in later showings it has turned white. Across his face and body there are several large scars. After his battle with Zi Shou , he loses his left arm and right foot, replacing them with human limbs that contrast noticeably with his blue-hued body.
Gui Mu's usual attire consists of a basic, loose black robe with long sleeves, worn over a blue shirt. During his battle with Fu Yi at the camp of the fallen ones, he instead dons a close-fitting black coat, trousers, and a mask which conceals the lower half of his face. He wields a large scythe.
Gui Mu is a sadistic and arrogant Great God. He despises mortals, viewing them as not only vastly inferior, but also ungrateful and defiant. He believes they deserve to be punished for these transgressions, and takes it upon himself to enact punishment. He sadistically slaughters any mortals who oppose the Gods, sometimes collecting their skins. After sustaining severe injuries during his battle with Zi Shou he begins devouring mortals in order to hasten his recovery. He cannot understand why Li Jing would oppose such practices.
Though appearing almost irredeemable, Gui Mu does seem to possess some better qualities. He is not unfair, shown when he pardons the decieved Li Jing for attacking him, and agrees to help him find his son, Ne Zha, after the latter is kidnapped by Wu Geng. He also adopts the mortal prince Ji Qiao as his godson and requests that Li Jing train him in the art of Smelting Aura, though his motivations for doing so are as yet unknown.
- Poisonous Locust Swarm: Gui Mu summons massive swarms of poisonous locusts. A single bite can slow an enemy's reactions considerably, while multiple bites will result in death. Only the 5 others Gods of the Affiliations had the ability to counteract it; Zi Shou lays this to rest.
- Death Aura: Summons a dense barrage of extremely fast, deadly snakes which coil around the opponent and devour him.
Necrogen Mist: Creates a cloud of mist which disintegrates the bones of the body completely, killing anyone caught within it.
Venom Claws: His venom claws are extremely powerful, capable of paralysing an opponent in seconds.
- Tracking: The poison from his venom claws can never be completely eradicated and can be detected by his locusts, allowing him to track the location of any enemy he has poisoned.
Scythe: He is a skilled scythe user, demonstrating excellent melee abilities during his battle with Fu Yi, where he almost struck Fu Yi several times despite the seers vision of the latter.
Gui Mu joins Tian Kui with the Great Gods of the other five Affiliations, arriving via Tian's dragon. Outside Zhao Ge, he slaughters the Shang soldiers in delight, before losing his left arm to Zi Shou empowered with the Immortal Phoenix. He is in disbelief and then attacks Shou with his Divine Power out of anger. In the ensuing battle, he also loses a leg. He is greatly weakened by his injuries, and the other Gods consider his defeat a disgrace, tarnishing his reputation.
However, the prince of Zhou, Ji Qiao, comes to Gui Mu's aid and builds him a healing chamber. Ji Qiao procures children for him to feast upon in order to recover from his wounds. Over the next five years, he feasts upon countless humans, and becomes more powerful than he ever was before. In doing so, he discovers that it is possible to replace his lost limbs with limbs belonging to dead mortals.
As a reward for serving him, Gui Mu adopts Ji Qiao as his godson and grants him his wish to learn the Smelting Aura technique under Li Jing. However, while Gui Mu is at the Northern Mountain Mine, Wu Geng turns Li Jing against him using deception, and they fight to a stalemate before Ji Qiao discovers the truth and intervenes. Gui Mu hunts Wu Geng and almost kills him, only to be prevented by the arrival of Fu Yi, Gui's former master.
Gui Mu later arrives at the hidden headquarters of the Fallen Ones, leading the Beast Legion. He reveals that the poison he implanted in Wu Geng's body during their battle at the northern mines emits a faint odor which never fades and allows him to track the victim for the duration of their lifetime. He engages Fu Yi in battle once again, before Fu Yi is defeated by the arrival of Tian Kui.