Dark Energy (ダークエネルギー) is a special type of Ki that exists in the Demon Realm and the Makyo Star, and is naturally possessed by members of the Demon Realm race. Being in contact with this energy can allow an entity to power up greatly, though too much Dark Energy will often cause those who are not a member of the Demon Realm race or a Makyan to go berserk.
Dark Energy is greatly beneficial to demonic entities and makes them far more powerful than normal. Dark Energy can power up evil beings, which usually causes their personality to become more ruthless. In some cases it can grant transformations, as it allowed the demon Towa to take on her race's Dark form, and allowed the Spice Boys to undergo the Makyan Gigantification transformation. A Demon God can use Dark Energy to take on the Giant Demon God form.
This energy normally only exists within the Demon Realm and Makyo Star, however the Ki can be spread outside of those locations by members of the Demon Realm race, which is often used to try and corrupt multiple worlds.
Due to its demonic nature, Dark Energy has a dark or sinister feeling compared to normal Ki which can be felt via Ki Sense as noted by several characters.
Video Game Appearances
In Dragon Ball Heroes, Dark Energy is used by several characters to empower others. Demigra uses it to brainwash Great Ape Gohan during the Dark Demon Realm Saga, and the Dark Dragon Ball Warriors use it to empower their henchmen during the Dark Empire Saga. Towa uses it to brainwash the Dragon Team of Dragon Ball GT during the Dark King Mechikabura Saga, and later Demigra gives Dark Energy to a defeated Dark Broly to revive him as a mindless berserker.
In Dragon Ball Xenoverse 2, it is implied that this energy corrupts and augments the Fruit of the Tree of Might turning it into a demonically enhanced strain that can grant consumes the power of Villainous Mode and even cause their bodies to swell with Dark Energy and with further modification can be used to cast a new type of spell on the consumer that grants the first stage Supervillain power-up after shaving off the recipient's life to unlock greater power. Due to his status as a Demon Clansmen, Dark Lord Slug is able to sense this pure dark energy as it surges through his body before he becomes Supervillain Lord Slug.
"Nrgh...! N-No. It's Hirudegarn... He stirs! The beast's lower half must be nearby! Wait-no! Hirudegarn... is responding to the dark energy pervading this place. His return will spell certain doom for this world! The evil energy must be dispelled. Will you aid me?"
— Tapion noting the Dark Energy is weakening the seal on Hirudegarn in Dragon Ball Xenoverse 2
In a parallel quest, the Dark Energy of the Supervillain form causes the upper half of Hirudegarn that is sealed within Tapion to stir and must be dispelled before Hirudegarn can break free indicating that demonic entities like Hirudegarn can be strengthened by simply being in the presence of the pure dark energy emitted by the Supervillain form or that it somehow weakens the seal that keeps Hirudegarn's upper half contained.
In Dragon Ball Heroes: Ultimate Mission X, the Dark Energy is featured heavily in its story mode where several non-Demon Realm race villains use it to acquire the King of Destruction form after they are defeated. Demigra gives his dark energy to Chamel near the end of the game with the intention of causing Chamel to go on a mindless rampage and destroy reality, but Chamel resists the corruption and refuses to use the Dark Energy.
In Super Dragon Ball Heroes: World Mission, Demigra secretly provides some Dark Energy to Xeno Turles after he is defeated in the side story "Note's Adventure", reviving him and causing him to go on a rampage. Babidi's Forces are powered up by Dark Energy due to Sealas's anomaly, as are the Cell Jrs. created by Ahms. During the Extradimensional Space of "Hero Town in Danger!", the Dark Energy of Babidi's Forces resonates with the sealed Hirudegarn, allowing him to break free from Tapion and Minotia.