The Black Blood is a substance that exists in the Kingdom Hearts Fanfics Darkness and Light and Reigning Shadows made by Evnyofdeath. It is similar to regular blood with the exception of being black, and it also possesses the ability to drive those who possess it insane by feeding their inner Darkness.
The Black Blood is shown to be able to drive even the reserved insane as shown with Yami. It also grants those who possess it supreme control over the Darkness as seen with both the Empress and Yami. It is revealed in the case of Blaid that if they use their Insanity as a form of controlled Beserker State it wouldn't control their actions, the Empress/Ulmia has limited control over her Black Blood, not to the level of Blaid whom was born with the ability.
Later it is revealed that whenever someone is recruited by Blaid and his blood is injested to force the awakening of their Black Blood, they gain the "Black Spot" which they carry at some point on their body, this spot is black in nature and if glared at seems to look like it passes all the way through their body.
The "Black Spot" seems to have been made from Blaid's ancestors, it forces the Dark Keyblader in question to be totally loyal to him and his family line, without question and it seems to be unremovable without killing the person and destroying their heart however one other means is for the one whom awakened the person's Black Blood to transition their Heart into that Body however that ability is only possible if the one transitioning doesn't have a Black Spot either.
Blaid Dark has been found to be a Black Blood "Pureblood" (sounds a lot like Purebred), he has been known to use the Black Blood to his advantage rather than have it weakening himself. See: Blaid Dark - Abilities - Black Blood or Blaid Tenebrae.
Those of the Dark/Tenebrae Family and Realm In-Between Nobles are opposite to the Princesses of Heart or those with strong Lights in their Hearts, this gives the possibility that those with High Ranked Black Blood or linked to someone with High Ranked Black Blood are immune to Heartless, whom hunt the Darkness in the Hearts of others.
In Fanfictions by EvnyofDeath
The Empress tells Yami in the last chapter of Darkness and Light that it is estimated only 3 people out of all the worlds possess the Black Blood, or a functioning version anyway. The following is a list of those who have it within the Realm of Light:
- Empress of Darkness
Presently however, it is revealed that there are others with the Black Blood lying dormant within them, the remaining Black Blood Wielders whom possess functioning Black Blood outside the Realm of Light:
- Blaid Dark
- Toru Marek
- Tormack Dark
- Shinji Shade
- Rex Sheder
- Possibly other Dark Keyblade Wielder and Apprentices.
In Fanfictions by Blaid
Black Blood in the Third War Between Darkness and Light is rather unknown, it is discovered that everyone with Strong Light within them has a hint of Strong Darkness and Black Blood, making a Strong and Humanoid Unversed if nurtured. Those with Black Blood are:
- Blaid Tenebrae
- Shadow Obscurus
- Tormack Tenebrae
- Yami Tenebrae
- Ulmia Tenebrae
- Sol Requiem
- Rufus Shinra
- Vayne Solidor (awakened by Blaid)
- The Black Blood is based off of the substance of the same name from the Anime/Manga Soul Eater, and has similar effects such as driving those who possess it insane.
- It seems that the theory of Blaid gaining his apprentices from the Realm of Light is true, however he goes after those whom have dormant Black Blood and takes them to the Pro-Dark Realm In-Between, it is unknown if he can grant this power to those who don't have Black Blood or those whom have somehow injested Black Blood and gained some of its effects.