The Realm Between is the third realm and lies on the boundary between the Realms of Light and Darkness.
Few worlds exist within it, and most have some special nature or purpose Each world ties closer to the Realm of Light or the Realm of Darkness and some that is in it.
The Lanes Between are a series of "roads" between the worlds in frequently use these paths to navigate the worlds. The presence of Darkness is very strong within them, forcing travelers to wear their Keyblade Armor as a safety precaution.
To enter the Lanes, the Keyblade wielder raises his or her Keyblade to the sky, and creates a portal leading into the Lanes Upon opening the way, they usually call their Keyblade Glider.
Pureblood Heartless are natural Heartless, born from the darkness in people's hearts. They are ink-black in color, with yellow beady eyes.
They are more common in places that are close to or saturated in darkness. Upon their destruction, they simply disappear in puffs of darkness, without a heart leaving its body.
Emblem Heartless, on the other hand, were originally created from machine's that reproduce the process of a heart being consumed by darkness.
Afterward, stolen hearts can become Emblems. They have more varied shapes, colors, and are branded with symbol to differentiate them from the Pureblood ones.
They are more common on the worlds within the Realm of Light, and usually mimic the shape of creatures or objects within that world.
Heartless, Emblem or Pureblood, possess several key characteristics that define them as Heartless.
All Heartless are created when the darkness that resides in a person's heart consumes him or her, thus giving the darkness shape and form (this process occasionally forms Nobodies, which are born from the body and soul left behind when the heart is lost).
Being born from darkness, they are mindless and act on instinct, their only goal to find hearts, and consume them to create more Heartless but, what they desire above all are the hearts of worlds, and thus they enter worlds in search of the way into the hearts of the worlds. When they consume these colossal hearts, the remains of the world form new worlds.
At the same time, Heartless seek out the users of the Keyblade, since the Keyblades are able to vanquish Heartless very effectively.
In order to stop the users of the Keyblades, the Heartless use the Keyblade itself as a homing beacon, but ultimately desire to take the heart that commands it because of this, Keyblade wielders are under constant attack.
Heartless, being formed from darkness, have varying strengths, depending on the amount of darkness in a person's heart. The darker the heart forming a Heartless, Emblem or Pureblood, the more powerful and more monstrous the resulting being will be.
This is a direct contrast to Nobodies, which determine rank according to the strength of the heart, and whose appearance becomes more human as they increase in power.
The Heartless, being mindless, usually have no master to direct their actions and instead act on the instinct to gather more hearts.
However, there are some higher beings who can command them. Heartless will obey those with an affinity for darkness and a strong will. If many people attempt to control them, the Heartless will side with whomever is most powerful.
Those with hearts, endanger themselves however, as the Heartless are attracted to their hearts and if they show weakness, the Heartless will not think twice of consuming their hearts.
On the other hand, higher ranking Heartless, can fully command other Heartless without endangering themselves. Also, higher ranking nobodys is able to command them as well with their strong wills, but are not endangered of being consumed by them for their lack of a heart.
Heartless make use of the "corridors of darkness", inter-dimensional pathways that connect the many worlds. These pathways are located in the Realm of Darkness, and thus are very dangerous to use if one is not accustomed to the darkness.
Nobodies are born when a Heart is swallowed by darkness and becomes a Heartless. They are the remaining parts left behind by the heart: the body, giving a Nobody form, and the soul, giving the Nobody life.