"Are the Undead real? Take a look around you in this world filled with mysteries. What reason is there to believe they are not real?"
-Academy Teacher of Seireitei, name not known
For a long time, the whole existance of the Undead was considered nothing but a myth, because sightings of them could be considered more rare than a Vasto Lorde doing the Caramelldansen. However, as an urban myth, they always existed, in both the Sugiura Lands and Soul Society - men and women with the ability to shift into a monstrous form of destructive force, and a wonderful form of a majestic beast able to conjure amazing powers.
However, it was only over the last 30 years, that these beings really started to turn up and make themselves visible. Living hidden from all societies for almost all the time, only the current Queen and King of the Sugiura knew of their existance. These beings gave themselves one name: Undead.
An Undead is a lost soul, a Plus, fused with a Guardian Beast. But since normally a Plus can't enter the Sugiura Lands and Guardian Beast plains, their existance should be impossible. However, whenever a soul is send to Soul Society with Soul Burial against their own will, there is the chance lingering Reiatsu will interfere with the sending and spiral them off into another dimension. Lately though - in the last centuries - spiritual phenomena can also simply absorb them from the real world into another dimension. Most of the time, they land in Hueco Mundo and get eaten. Only a very small percentage actually lands in the Sugiura Lands, and even less manage to fuse with a Guardian Beast before they get destroyed by the environment of this dimension. Once the fusion occurs, the soul is forever removed from the soul circle.
Once a Guardian Beast tries to attack a Plus, they can and will fuse together, forming a monstrous form. Sometimes this menancing beast almost looks humanoid at first view, but cleary isn't one. They always seem to have a certain animal theme, like bird or grasshopper, with vicious natural weapons, and little intellect. The first thing a newborn Undead will do is rip open the fabric of space and time, and slip into the real world. There, the monster will search for the original body of the Plus part. Only if they manage to find this body and completely destroy it, they will stay in existance, and not simply vanish forever.
Once the original body is destroyed, the fused being regains their mind, and humanoid form. Their memories are often whirled together, clouding exact things and making the life before seem like a dream. This is called 'the Awakening'.
It should be noticed that after the fall of Aizen, more and more Undead start to either exist, or show themselves. It seems like the sudden rise of such a gigantic force of spiritual energy and a fall just as quick did lead to a disruption of the dimensional fabric, and made it easier for a Plus to slip into the Guardian Beast Plains.
Powers & Forms
"Our powers are like the stars - no two are the same."
-1st White Joker
A Guardian Beast normally gives a Sugiura the power to assume forms, depending on their Reiatsu and training. However, Undead are one being fused together, their powers work quite differently. In human form, an Undead can use weak level Sugiura sealing magic, and low level Kido, up to level 20, to be exact.
The next stage all Undead can access, but not all can master, is the Monster Form. This resembles a Shinigamis Shikai, and grants the user special elemental, magical, or physical powers, based on what Guardian Beast half they have. Their powers are just as wide-spread as a Guardian Beasts.
Finally, the strongest of the Undead can enter a stage known as 'Guardian Beast Form'. But they don't simply change into the GB fused with them, but rather, into a humanoid, highest level Guardian Beast. In this form, their powers are increased dramatically, even a bit stronger than regular Bankai. They can fuse together with a Sugiura for a short amount of time, to increase the potential power of both, granting them two Sacreds at the same time. However, this power comes with a great price - only a short time can be spend in this form, or the Reiatsu of the Undead will run out, and he will cease to exist.
Lastly, all Undead have one power the same, called the 'Dead Eyes'. It is impossible to decieve one of the Undead with an illusion, no matter what kind - they simply have no effect on them. This ability is always in effect.
Order and Moral
"As fleeting as the clouds, as disorted as the winds, but always strong like a mountain. This is what we are."
-First Undead, 'Original'
The personality of an Undead is usually a mixture of Plus and Guardian Beast, but since most fused beasts are very feral, just as many stay nearly the same, but with a wilder and more outgoing persona. In fact, the normal Undead will seem not really 'undead', but more like a very happy and energetic person. This is one of the reasons why they could hide for centuries and millenia.
However, this is not always the case. An Undead can be brutal, proud, cautious, a coward, a hero or a villain - not two are the same. However, all Undead have a 'Rank', and a certain natural instinct not to harm their race, even though they have no goal together or real organization most of the time. The last meeting of the Undead was over 500 years ago.
This instinct makes it still possible for two Undead to hate each other, or for one to kill the other. However, every Undead would feel a strong personal rejection once their thoughts drift to harming more than 2 of their kind, and only the most mad of them all could commit such an act. If the culpirt is identifed, the White and Black Joker will bring the Undead to justice and kill him/her without mercy, as this is the only law the Undead have normally.
The highest ranks, as it was said, are White and Black Joker, and only those two are actually not just given out. When an Undead 'awakens', they sometimes do so with the Mark of Joker, but that only happens rarely. Once a new Joker marked appears, the corresponding Joker will step down from their role as spiritual leaders of their people, and pass their rank on, often serving as advisors for the new Joker at first. Almost all of them decide to pass on afterwards, leaving the known dimensions. Only few former Jokers remain. [A new character can only be made with a new Mark of Joker or be an old Joker if allowed by me, Silim, since they are exceptionally more powerful than normal Undead]
Otherwise, Undead lack ranks - unless they follow the order of the Ancestors.
While it is not mandatory for the Undead to join any organization, or follow orders, the two current Jokers are also always the leaders of what are called the 'Dead Apostles'. The Undead lack the numbers to fill a real organization with specialized squads or units, but they still band together to shape the worlds into what fits them and their eternal allies, the Sugiura, the most.
The ranks of the Dead Apostles are: True Ancestor (usually always a Joker), Dead Apostle Ancestor (only very old or powerful Undead gain this rank), Dead Apostles, which work directly under the Dead Apostle Ancestors, and finally, the Dead. Almost all normal Undead are members of the Dead even if only for self-preservation of being able to call upon help.
The main reason why there are only so few Undead compared to the magnitude of other people is not just the way one can become an Undead. While it is very rare for one to appear, no Undead can produce offspring of any sort - no matter with what race they try it. Over half of the existing Undead don't even feel sexual urges or pleasures to begin with. This is one of the main reasons why they are called Undead - Those who are truely dead can't give birth to new life.
Finally, those born with the Mark of Joker have it on the back of their hands (Black Joker) or on their left or right cheek (White Joker). Strangely enough, the Black Joker mark looks white, and the White Joker mark looks black, until their possessor uses Undead powers, after that they glow in their color till the wearer doesn't use the powers anymore.Roleplayers Notes:
Only the best informed characters know of the Undead, and even those are surprised they exist. The only exceptions are the current Queen and King of the Sugiura, since both know the current White Joker. Otherwise, it's the usual. Don't know their powers before they use them, etc.