This theory is not original
This theory is long..but its very good if you read it..^_^
It all starts with the rinegan. The rinegan means Metempsychosis eye. Metempsycosis is the belief of transmigration of the soul. After death, ones soul eventually ends up in another being whether it would be plant, animal, human etc.
This ties with the belief of the Bhavacakra. The six realms of existence.
The world of Devas(gods)
The world of Asuras(demi gods, titans)
The world of Humans
The world of Animals
The world of Pretas(hungry ghosts)
The world of Hell.
How does this tie with the rinegan? Well, the soul is meant to roam free, but is bound by the body. After death the boundry is destroyed, meaning the soul can roam free but it is eventually trapped in the never ending cycle of rebirth.
Now my theory is the rinegan works even after death, giving the person a new life. According to the metemphyscosis, if ones life is high and and good they will be even higher up in the next life. They will usually have on their body or in their mind a relec or memory of their past life.
Now, it starts with before rikodou was born. It starts with an animal. This animal died but would later on be reincarnated into a higher soul. This is when rikodou is born.
Notice the ear like figures? Maybe a relic of his past life. Now whether you believe if he was reincarnated ffrom an animal or not then it does not matter because he was incarnated from somewhere, but it doesn't really matter the next part does.
Okay, so all we know of rikudou is that he invented all ninjutsu. Because of this deed he would be reincarnated even higher up in his next life. Now you may be wondering, why did it take so long for him to be reincarnated? Well for some beings if they reach a celestial point they will escape the neverending cycle of rebirth, but because of the rinegan he is destined to be reincarnated. Some souls can wander around for years but will always end up back in the cycle.
Ok, so many years later Nagato was born. Having the rinegan. If you look back at the picture of rikudou he has similar hair styles to Nagato. A past relic of his former life. Also, the rinegan allowed him to master ninjutsu, maybe becuase of his past life, rikudou inventing all ninjutsu, this eye kept his abilities dormant until Nagato needed it. I also believe the rinegan keeps all former abilities of its former user, but since only rikudou had it first then we might never know.
Nagato was born as an Asura. A demi-god. But it is not as great as it seems. Demi-gods are born to be unhappy. Later on we know Nagato loses his family.
Demi-gods also are destined to be passionate, meaning they have good intentions. Nagato's intentions are to make everyone live in peace.
but, they eventually carry out their motives wrongly. Pain carries out his motives in an irresponsible way.
Wikipedia states that Asuras have the same mental state as a human, always obsessed with violence and force. Explains Pain pretty well. Pain is an Asura, not quite god, not quite human.
Whether of not Pain remembers anything of his past life is unkown, it is possible. But we do know that he posseses the rinegan, the eye that reincarnates to the next life. People may be wondering, why would it reincarnate itself? Well it is a tool of heaven meant to bring salvation to the world. It would be pretty chaotic if we had a bunch of people walking around with the rinegan. So to keep it balanced the rinegan is reincarnated to a generation that is in complete crisis, and as we know Nagato was born during a war.
Peins other true purpose.
The next part of my theory is that Pain has recieved Bodhi. Bodhi is enlightenment. It is complete and perfect sanity or awareness of the true nature of the universe.
Pain is aware of what the world is coming to. Pain wants to end all wars so that he carries out the rinegans purpose and that he recieves englightenment. After he recieves englightenment he will be cast out of the rebirth cycle. The rinegan would have no purpose anymore, and after recieving englightenment he will never be reborn again and will never have to suffer another life.
Bodhi also states that one will give up on dreams and realize reality. In other words Pain has given up on his dream of obtaining peace and is now in reality, he wants to end wars the only way he can. Bodhi can also be described as spiritual awareness. This may be another reason why Pain calls himself god. More proof that Pain has recieved englightenment is in the factors of englightenment. There are groups of factors that point towards englightenment. The first is this
Contemplation of the body (kayanupassana)
Contemplation of feelings (vedananupassana)
Contemplation of consciousness (cittanupassana)
Contemplation of mental qualities (dhammanupassana)
Contemplation of the body means to seperate ones self from the body. As we know Pains original body, Nagato is nowhere to be seen.
Contemplation of feelings is to rid ones self of feelings, Pain has no feelings and does not seem to care for anyone.
Contemplation of consciousness means to rid yourself of your conscious, Nagato felt bad for killing that chuunin but Pain feels no remorse for killing anymore.
Contemplation of mental qualities means to rid yourself of mental qualities, well Pain did'nt really have any to start with.
Anwyays after recieving enlightenment Pein becomes a devas(a god, celestial being) and has extraordinary powers now. This is where the six bodies come in.
Devas are invisible to the human eye. They have the power to insert their souls into lower beings.
Meaning that Nagato's soul is invisible but manifests intself within the six bodies that it choses, this also means that Nagato can switch the host when he loses a bodies function, each of the bodies lives within different realms. Nagato being the devas. Which ones they live under is not known at the moment.
Pain says he has evolved from a human into a god. Asuras share the same mental state as humans, so when he says i have evolved from a human into a god, he really means he left his human mentality and became celestial.
Devas aren't completely superior to other beings, but they have unusual abilities. They can still be killed but may live for longer periods of time. With Pein, it could be 100's of years because the bodies he's in are already dead.
Forgot to mention..if you would examine this closely..if pein really is the reincarnation..it makes sense about the "6 Paths Of Pein" and "Sage Of The 6 Paths"..what if pein is the reincarnation of the rokodou sennin..stated in my theory that he will be reincarnated in a time of crisis..reincarnated as nagato..nagato being in akatsuki and being called pein..made the "6 Paths Of Pein" and therefore we can call him now the "Sage of The Six Paths"
If You Read Naruto 419..You Could See That The Realms On My Theory Existed..Oh My God..!!