The Dark Abyss

The Dark Abyss, alternate known as The Void, is the name for the world entered by Claymores to sense anything else with yoki. The dark abyss is a pitch black void with the exception of lights which indicate the presence of yoki, and is a timeless dimension above reality. This dimension serves as the source of all Yoki, and contains infinite possibilities. Individuals with improved yoki sensing ability (Eyes and warriors like Samara) can see more detail such as waves and unique designs rather than just lights. The only warrior unable to do this is Grace who enters her red-world instead of the Dark Abyss when she tries to sense. If the prophecy of Nexus is true, this void is Aezathol's existence, and she has complete authority over it. The dark abyss is in fact canon and is seen when Clare meets Rafaela and fights in a mental battle with her, when Clare awakens Teresa's latent power, and when no 6 Renee was forced to poke into the destroyer's mind by Riful.

The dark abyss is both a personalized fragment of the void, the power tapped into when using yoki, and the individual's heart of yoki itself (yoki is a fragment of the void). This is evidenced in chapter 20 where Iris enters this world by focusing on her heartbeat with yoki perception, the center of her yoki. Inside this world, the representation of the individual is a combination of mind (which gives the soul a specific form), soul and yoki. This is further evidenced  by  Zero 3's claims that a loss of a battle in the Dark Abyss would destroy the mind. Since awakened have their yoki surrounding their souls, their yoki and therefore their awakened forms show in the Dark Abyss.

The Dark Abyss contains all the mental worlds of all yoki-using beings. Seen from an observer's prospective, these worlds appear as bright lights in the void, allowing for yoki perception.

Grace herself has a dark abyss but she can't enter it freely. It has been hinted that this is because of Aezathol herself blocking Grace from entering anything past the red world. This blocking appears to be part of the reason Grace is unable to sense, the other being that she has no control over Aezathol, her yoki, and thus, cannot use Aezathol to sense other yoki sources.

Eye class beings can pull others into their own Dark Abyss to talk and synchronize with them. Fighting can occur within the Dark abyss and yoki can be used more freely than in the real world, amplifying combat abilities.

According to Blanc, the Dark Abyss is where the yoki can combine with the soul of the user and evolve. With this in mind, it would stand to reason that all of the abilities and Grace's power (Aezathol and the souls she has sacrificed) are kept in the dark abyss.

Here is the order of appearance between the worlds:
 * 1) Reality
 * 2) Red World/Blood Mist borderlands - The Mental World Mixed with reality
 * 3) The Mental World- A personalized world of yoki, seen as a light by observers looking at the yoki from the Dark Abyss.
 * 4) The Dark Abyss-the void itself.
 * 5) Possibly a dimension above the Void, or a higher/deeper level of the Void, separated from lower/shallower parts of the Void by a distinct cutoff.