Origin of the Monsters
Millions of years ago, when dinosaurs used to inhabit the Earth, many other ancient species inhabited the Earth as well. These other ancient species are what we previously recognize as duel monsters. It has been recently discovered that today's duel monsters were in fact the real deal at one point in time. Of course these "duel monsters", as we know them, were more unique and more powerful than the already renowned dinosaurs. When meteorites and comets started to ravage the Earth, many beasts used their unique abilities to avoid and survive the damage and destruction. When the worst was done and over with, life eventually started to develop again. This time evolution decided to invent a new kind of animal, humans.
As man eventually evolved into being, humans started to grow and become more intelligent and destructive in their nature. Humans soon figured ways how they can suppress these mighty beasts through many methods of various magic's, or any kind of form of spiritual power/energy. There has been recently discovered ancient records of a civilization from about 15,000 years ago who have practiced with what may be believed to be the first now known form of magic, researchers have interpreted it as "twilight magic". Little is unknown about the tribe itself who formed this magic, but it is known that the method of twilight magic was used to mingle the spirit of a human host with the spirit of the chosen beast.
Reasons why the souls of these beasts were being mingled with human souls was because the ancient civilization believed that the power of the beast would help protect the tribe from neighboring enemies. The beasts that were chosen to be hosted were mainly dragon species because they were the most powerful, such as the blue eyes white dragon and the red eyes black dragon. Other weaker beasts such as kuriboroh were sealed into simpler things like instruments of combat or in shrines. As this twilight magic developed further, beasts and humans were not just sealed together spiritually, but even down to a cellular level. Ancient burial sites have shown that this development may have been unsuccessful cosmetic and lifespan wise because of deformalities. Although, that does not mean that the mutated gene was not carried on because other burial discoveries have shown the same characteristics. It is apparent that the mutated gene started to recess and stabilize throughout generations. In other burial sites that were a little more recent barely showed any of the mutated gene.
At first, researchers could not figure out what had happened to the mutated gene. Forensic and genetic scientists discovered that the mutated gene did not disappear, but perfected and remarkably became a "were" gene. As in were-wolf, were-cat and so on. A were gene is a gene that stays silent and dormant until subjected under certain environmental conditions (like in a were-wolves case it is the moon). Back to the discussion, when the were gene is stimulated, the individual undergoes a series of rapid cellular changes and can shortly convert into their designated monster. Every type of were gene has its own unique characteristics which helped determine exactly which beast or duel monster that the cells need to duplicate. Depending on the original nature of the monster, such as lightning is to the Blue Eyes White Dragon, the lightning element will be the trigger for the genes stimulation.
Of course, the stimulation of this gene takes a lot of stamina and energy so total exhaustion when the individual changed back to their original form should be expected. Years of cardio and strength training may have helped prevented these individuals from becoming vulnerable afterwards. Looking deeper into this gene, there is even more to it.
There are suspected two types of this were gene, a carrier type and an expressive type. Carrier types are completely recessive, they can only express their were gene through spiritual (mental/physiological) stimulation which only provided a sort of simulated magical projection of their inherited monster. Carrier types cannot perform the exact changes described earlier (carrier types can still inflict harm with their simulated monster), which has scientists debating whether the carrier type or the expressive type is the true form of the were gene because the expressive were gene does express all of the changes.
There has recently been a journal discovered in the pharaohs tomb written by a high priest of an individual named Kisara. As Kisara is described in the journal, Kisara seems to be a good example of a carrier type. Expressing your were gene when you are a carrier type is risky because a part of your soul as well as the soul of the monster physically shows and that would leave skilled magic users a chance to seal that power and use it for their own means. With parts of the soul missing, the rest of the individuals body is unable to continue; in other words, the individual goes into a terminal coma.
As for the expressive type of the were gene, it is when the individual undergoes the cellular changes into their signified monster. There is no sealing of this gene type which is a major genetic advantage in a world exploring magic. The expressive type were gene is determined as a dominated trait. Although this gene has a great genetic advantage, it has rarely occurred repetitively between generations. After genetic simulations, scientists believe that it might be because the were gene cannot replicate with other expressive were genes because the genes originally did not evolve naturally into the human DNA code but mutated quickly into the Human DNA gene pool with the twilight magic.
This next part is where it will be useful to have knowledge of cell Biology because it explains how the were gene might occur throughout generations. When haploid were gene cells undergo mitotic division, that is where the carrier type were gene comes from. So the were gene is not completely lost, it is simply carried. Only pure un-tampered human DNA can assure the recurrence of the expressive were gene type because the were gene doesn't have another were gene suppressing it; keeping it from making an expressive type, but just another carrier type. Scientists also discovered that haploid cells of two completely different were genes or two different monsters do not undergo mitotic division, therefore there is no chance of reproduction between two were genes possessing different monsters. It will almost seem that the two individuals are two different species.
After countless experiments to further discover the were gene, scientists have discovered that the gene is very resilient against other genes such as un-tampered human genes. There is still chances that different alleles from the parents are still randomized, but the mix up of alleles do not seem to delude the were gene. Therefore, the were gene can be passed down many times over without being faltered. So it is hypothesized that today, the were gene maybe a part of millions of people today or the gene may have taken a turn for the worst and died out. Many scientists had agreed that the gene may have died out because of an unfortunate use of a dark magic used by the Egyptians 5,000 years ago.
Before going into detail about what happened in Egypt, take note that by this time the individuals with the were gene have formed their own distinct tribes therefore tried to keep their genetic heritage within their tribes. Each tribe was different from whichever monster they were. After a while, all that resided in these tribes were carrier type were genes, and it had been a long time since there had been an expressive type were gene because tribes wanted to keep their bloodline untainted. Sounds gross, but understand that way back then no one understood what genetics was or even knew what DNA was.
By this time in Egypt, because of long generations of carrier types, there was prior knowledge about their disadvantage to skilled magic users and people who believed that "those who possess the power of great monsters" could be captured and their powers used for war and combat. The magic used was soon called shadow magic, and powerful magic users used this shadow magic to start sealing the powers of monsters inside giant stone tablets regardless of the wellbeing of the individual. Use of the millennium items were what helped drive this process. Eventually, the use of these stone tablets gave birth to a competitive and life threatening system known as the Shadow Games. Series of gifted tribes started to dwindle down in numbers as countless souls were sealed away inside stone tablets. Many tribes broke up and scattered because magic users got so power hungry that they even started to target and capture small children.
People started to realize the cruelty into obtaining these powerful stone tablets and amongst the people who tried to stop the cruelty of sealing peoples souls was Pharaoh Atem. By Atem's time, the sealing of monsters were not as sever as when it first started, but it was still occurring. He sought to end the dangers of the shadow games, by the cost of his memories as Pharaoh.
As centuries past, the ruminates of the scattered tribes had spread across the world and generations of expressive type were genes were seldom reappearing. As humanity started to become more aware with moderation, individuals of the expressive were gene have created families and secretly communicated with others like themselves and developed a system where they can survive out in a modern world without having their powers discovered. Eventually, secret organizations became created. A general term then was discussed to help explain who and what they are, the different families agreed to determine themselves as Spirit Shifters, for they physically transform into the spirit of the monster they represent. Formally, they just identify themselves by family name, their element class, and name of their monster.
As the human world became more modernized in science and technology, so did the Spirit Shifters. It is discovered that Spirit Shifters express massive amounts of cellular activity when the moon is full. Something about the reflected solar beams from when the moon is at its brightest that cause the electrons in the chemical makeup of the were gene to become excited which cause more prolonged energy before, during, and after stimulation. So the secret community of Spirit Shifters organized a competition of speed and strength between riled up Spirit Shifters. They come to nickname this competition as "Dragon Wars". (ha-ha)
At first Dragon Wars was a competition to see who can last the longest in dog fights, but now there are many types of competition such as tests in speed and wrestling. There are even now simpler competitions for younger spirit shifters.
Since the dawn of the spirit shifter's union as a secret community, they have always stuck with elders as their leaders. As for where the spirit shifters are presently, their various clans and secrecy is as strong as ever and they continue to flourish under the nose of the rest of the world.