Yami's origins are unclear, as very little is said about him until the very end of the game, and his very existence is only revealed after Amaterasu confronts Ninetails at the peak of Oni Island. Ninetails describes Yami as being "the absolute ruler of all evil beings" and "the ultimate symbol of darkness". In Ōkamiden it's revealed that he had been the vessel of darkness for Akuro, likely willingly, given the dark spirit's unusual reverence for the demon.
It is believed that Yami and his demonic legion were being contained within the Ark of Yamato, though Waka was unaware of this when he brought the Ark to the Celestial Plain, fleeing an unknown catastrophe that wiped out the Moon Tribe, which also seems to be caused by Yami. When True Orochi later attacked the Celestial Plain, Waka evacuated the Celestials into the Ark and departed for safety. After they fled, Yami's endless legion of demons attacked, causing the event of the Ark of Yamato genocide, and the ark crashed into the mortal world soon after.
Two hundred years later, after Amaterasu and Oki vanquished Lechku and Nechku atop Wawku Shrine, the dark spirits of the twin demon owls merged with the essence of the previously defeated demons (Spider Queen, Crimson Helm, Orochi, Blight and Ninetails) and moved toward the Ark of Yamato. Later, Oki returned Kutone to its pedestal beside Laochi Lake. The moment the sword returned to its place, a silver light shot forth from it, melting the perpetual ice of Laochi Lake. Then the ark emerged and opened a rainbow path down to the pedestal. Amaterasu can board the ark, but Issun can't. Within the Ark, after engaging in rematches against Spider Queen, Crimson Helm, Orochi, Blight and Ninetails, Amaterasu advances forward to battle Yami. It is revealed that Waka has been trying to battle Yami, but to no avail, as his attacks left barely a scratch. As the eclipse of the Day of Darkness completes himself, Yami awakened, and drained Amaterasu of all her Celestial Brush techniques, then blasted Waka off the arena, seemingly to his death. Nonetheless, Amaterasu engaged in a long battle, regaining her powers as the fight progresses. Finally, Amaterasu seemingly defeated Yami, but then an illusion of Issun appeared, distracting the Sun Goddess from the recovered Yami. He grabbed Amaterasu, drained her of her Celestial Brush techniques, again, but this time, Yami destroyed the techniques' respective constellations. All hopes seemed lost, but then Issun, who had realized his destiny as a Celestial Envoy, spread the words of Amaterasu's deeds to the people of Nippon, thus restoring their faith in her. With her powers restored by people's faith, Amaterasu regained her full strength, and annihilated Yami for seemingly an eternity . Then, Waka emerged from the depths of the Ark of Yamato, alive. He and Amaterasu returned to the Celestial Plain, restoring peace and harmony to the world.
Nine months after the events of Ōkami, darkness had suddenly returned to curse Nippon with its dark grip, and Amaterasu's son, Chibiterasu, came to dispel the darkness. Later, during the climax of his journey in the finale, it is revealed that upon Yami's destruction, Akuro fled from his body and its power was split and bestowed upon five other entities (Master Anura, Bullhead, Sen, Ryo, and King Fury), leaving the spirit greatly weakened. It proceeded to use Chibiterasu to help it recollect the four essences and complete himself with a vessel of light.
At first glance, Yami appears to be a mechanical sphere covered in arcane, Moon Tribe-like markings. As shown when Amaterasu fights the Lord of Darkness in the Ark of Yamato, the sphere is capable of altering itself into different forms, including disc-shaped platforms, a slot machine, a humanoid figure with whip-like arms and a giant clawed hand. Each transformation appears to change the shape and colors of the markings on Yami's body.
Yami's true form is that of a small pale fish contained in a glass ball full of water. His body bears markings similar to Amaterasu's, but colored blue instead of red. This form is usually hidden within the larger mechanical sphere, and serves as Yami's primary weak point during the battle.
"This horrifying entity has been called 'Empty Death'. It seeks complete destruction. For eons, it has been locked in a struggle with the sun god. This fight has been described thusly : Yami's destruction was countered by the sun god's Rejuvenation."
"Round, cold, and desolate as the moon, Yami has never been depicted as a human or animal in any drawing. It is simply too inorganic in appearances to warrant such portrayals. Yami took on a ring form when attacked, rendering blows useless. The beast was bathed in moonlight, the light acting as a blade."
"In most legends, gods are portrayed as good or evil ; as representations of specific animals. This is not the case of the dreaded Yami. Yami belched fire and ice, but the god deflected the onslaught. The beast attacked violently, with speed and unpredictability. Only by slowing the flow of time could the sun god defend itself."
"Its inorganic nature resembles machinery, leading one gadgetry expert to speculate that is is likely the source of all machines. When the god attacked with thunder, the machine coughed forth a seed. When the beast drew it back in, the god knew it must be the core. The beast tried to seal away its core with an icy blast."
"In all these tales, there is no record of a decisive victor. Has no one emerged victorious ? Or was the event simply not recorded ? As the darkness tries to cover all, forget not the warmth of purifying light. Prayer is power. Power is prayer"
Yami begins the battle by stealing the power of the Celestial Brush from Amaterasu, which removes much of her power and leaves her unable to wield her Divine Instruments. Yami's first form will attempt to smash Amaterasu with either a hammer or his own body, often leaving giant holes in the ground when he misses. Amaterasu must strike Yami a certain number of times in order to stun him.
After the Lord of Darkness has taken enough damage, Amaterasu will regain the stolen Rejuvenation technique, as well as her Divine Instruments. Any holes in the floor can now be repaired, though Yami is still capable of creating more. After dealing more damage, Amaterasu regains the use of Power Slash, which can increase the amount of damage she deals to the boss, and soon after she recovers the Greensprout techniques. At this point, stunning Yami will bring up a prompt to use Bloom, which opens his shell and reveals his core. Amaterasu can attack Yami for as long as possible before Blooming Yami to maximize the damage dealt.
After his health is depleted, Yami will transform into a green-marked form that can separate into platforms. In this form, he mainly attacks with fire, either by igniting his entire body and bobbing around the room, or by attacking Amaterasu with a single flaming platform from his body. When he separates his body, his core will be present on a random platform, vulnerable to attack. However, Yami can crush Amaterasu between the sections of his body if she doesn't jump off quickly enough when his platforms recombine.
Dealing some damage to Yami's second form will force him to release the Cherry Bomb technique. Afterwards, when Yami becomes stunned in this phase, Cherry Bomb can be used to blow apart his shell and expose his core. The Waterspout technique is the next to be recovered, which Amaterasu can use to stun Yami by extinguishing his fire attacks.
Crescent is the final technique recovered in this part of the battle. After stunning Yami again, using Crescent will summon an apparition of Susano, who cuts Yami's shell in half to expose his core.
Yami takes the form of a blue-marked slot machine in this phase. When he exposes his reels, Amaterasu must stop their spinning with a Power Slash. When the reels stop, Yami will assault Amaterasu with a barrage of attacks, with the attacks being determined by the symbols displayed on the slots: a snowflake for icicles, a flame for fireballs, a lightning bolt for lightning-imbued orbs, and a Lockjaw for cursed fruits, used by Cursed Trees and Bud Ogres. These attacks can be deflected back at Yami with Power Slash in order to damage him slightly. Yami's other slots include a bomb symbol that releases a bomb, which can be ignited with Inferno, an Ink Pot will make Yami releases Ink Pots, and a Spirit Globe will make Yami releases Spirit Globes.
After taking enough damage from deflected attacks, Yami's slots will display a blue circle when Power Slashed; this causes him to collapse and relinquish another of Amaterasu's Brush techniques. The first technique recovered in this phase is Galestorm, which allows Amaterasu to put out the fires left by the fireballs (including a barrage of flames that Yami will release immediately after losing his latest stolen technique). Next is Inferno; while it can't damage Yami, it can be used to melt any ice that has been left by his icicles or detonating his bombs - once again, the technique can be used immediately to counter Yami's recovery attack. Finally, Amaterasu regains Veil of Mist, which can help make lining up the reel symbols easier. Using Veil of Mist also causes the spirit of Queen Himiko to appear, who will drop several Spirit Globes for Amaterasu to heal herself with, though she will only provide Spirit Globes a limited number of times through the fight.
Once Veil of Mist is recovered, lining up three blue circles will expose Yami's core, rendering him vulnerable to attack. Deplete his health to force him to transform yet again.
In his new yellow-marked form, Yami sprouts a pair of short legs and two tentacle-like arms made of energy. He attacks both with his arms and with missiles, which can be deflected back toward him with Power Slash. A small hatch will occasionally open in the front of the sphere, revealing Yami's core and allowing Amaterasu to attack it. Yami can also fold up into a sphere and float across the battlefield while dropping a barrage of bombs directly below himself.
Catwalk is the first Brush technique recovered in this phase, though its only purpose is to allow Amaterasu to reach the top of a few pillars at the edge of the arena, where chests containing Exorcism Slips and Holy Bones can be found. After sustaining further damage, Yami will lose the Thunderstorm technique; following this, whenever Yami turns his arms into Ninestrikes or reveals his core, Amaterasu can stun him with Thunderstorm to make his core drop out. Using Thunderstorm on the dropped core will conjure an apparition of the real Rao, who will attack the core.
When this form is defeated, Yami appears to have been beaten completely. Amaterasu sees an illusion of Issun, which distracts her from noticing that her foe isn't truly defeated. Yami attacks the goddess, destroying the constellations of the Celestial Brush gods and making it impossible for Amaterasu to recover the techniques.
Issun, despite having stayed behind when Amaterasu went aboard the Ark of Yamato, senses that the goddess has been defeated. He makes the decision to accept his role as the Celestial Envoy, and tells the people of Nippon that the "white wolf" that has been helping them is really the sun goddess in physical form. Issun convinces them to pray for Amaterasu, and the power of their prayers revives her to full power, causing her to take on the form of Shiranui and granting her the Sunrise technique once again.
Yami's final form converts part of the sphere into a massive clawed hand connected to the rest of the sphere by a pair of short pistons. The core is now situated in the center of the hand's palm, protected by a small flap that periodically opens and closes. However, the flap will automatically close whenever the Celestial Brush screen is brought up, making it impossible to attack the core with Brush techniques without stunning Yami first.
At the start of this phase, the battlefield is cloaked in darkness, greatly increasing Yami's power; Amaterasu must use Sunrise to dispel the darkness and stun Yami, making him drop his core. After recovering, he will use his hand to attack Amaterasu with swipes, punches, and slams, as well as summoning volleys of missiles and firing a massive laser from his core. Periodically, he will also restore the darkness, which depletes Amaterasu's ink; as before, Sunrise will eliminate the darkness and stun Yami. After taking enough damage, Yami will finally be defeated.
- Yami (「闇」?; 「やみ」) means "darkness", "gloom" and "despair" (metaphorically).
- Prior to the battle, Yami is cloaked in total darkness, only revealing himself when the solar eclipse of the Day of Darkness begins; later, he adopts his final form at the same moment that the eclipse completes, with the sun completely covered by the moon. This may symbolize Yami defeating Amaterasu, as the villain's power is at his peak at the same time as the sun is completely obscured.
- Despite Yami's links to the Moon, Crescent is very effective against him because it summons Susano, who slices Yami in half with his sword, possibly because it gives moonlight, rather than blocking the sun as an eclipse does.
- During the first, fourth and fifth phases of Yami's battle, the missiles that he launches are actually oversized clay figures.
- In the Ark of Yamato, there are markings of Yami's final form. Also, in the concept art for the Ark, more of these markings are present.
- In Shintoism, Hiruko (「蛭子, 水蛭子, 蛭子神, 蛭子命, 蛭児」?; Leech Son God, Leech Son, Leech Son Soul (Soul means God or Noble here) Leech Baby, Water Leech Son), the disabled, unfortunate first son of Izanami and Izanagi, notably fits the characteristics of Yami including deformed, fetus-like appearance. In some cases, Hiruko was worshipped as the Son of Sun by the folks where Hiruko stranded. Hence Hiruko is also called Hi no Miko (「日の御子」?; Son of God of the Sun). In other cases, Hiruko is also called Ebisu and the letters 蛭子 can be read as Ebisu as well.
- Many fans in Japan pointed the similarities of Yami with Hiruko and considers that concepts of Yami include Hiruko's characteristics.
- Unlike Yami, however, Hiruko is not evil.
- Yami was the first woman in Vedic beliefs. She was a child of the Sun god and had a second name, YāmīnĪ, which means "night".
- In Tibetian beliefs, Yami is the goddess of death and rules the female spirits of the underworld.
- Yami's machinery appearance was based on Soranaki or KūBō (「空亡」?; Sky Decease, Void or Empty loss, Existence which equals non-existing, Unlimited Chi, Things are uncontrollable Chi which occurs against wills), the ultimate boss of Hyakki Yagyō. This can also be seen in the concept arts that Yami was originally named KūBō according to the Ōkami Official Complete Works. Legends of Soranaki was originally created through misidentification of the concepts of the Sun that banishes yokais, and Soranaki was created in the concept which regards "What if the Sun was actually a yokai?". Originally, Soranaki is the times in Sexagenary cycle when things won't work well according to the heaven, and Hiroshi Akamata later added the idea that the Sun appears during Soranaki.
- Soranaki was not well known among publics in Japan until the release of Okami, and misunderstanding of Soranaki as a yokai, or the strongest yokai, suddenly spreaded, even more confusing publics' understandings.
- Like Amaterasu, Yami is not able to speak. However, he appears to be capable of expressing rage.
- Yami appears as the main antagonist in Tatsunoko vs. Capcom: Cross Generation of Heroes/Ultimate All-Stars as the one responsible for merging the universes of Capcom and Tatsunoko with the real world. As the final boss, he uses his first, fourth, and final forms from Ōkami.
- Yami is likely influenced by the East Asian deity Yama, also known as Enma/Emma King of Hades, or King of Evil, or god of death; however, Yami does not share a visual resemblance to the god Yama.
- According to Ōkami Official Complete Works, Yami was orginally called Empty Death during the design phase of Ōkami.