Amidaru is the firstborn son of Ninigi-no-Mikoto and Asanohana Asakura. Born into an era predating any form of chakra, Amidaru became one of the most powerful shamans to ever live. Shortly after birth, the Asakura clan labeled him a "cursed" child who bore the power of a long forgotten entity. With its power, it could rip the life from a planet, passively read the mind of any human it desired and much more.
Amidaru's clan all agreed they could feel the evil presence within him and knew that it had been reincarnated into the boy. Knowing nothing good would come of the one who bore the power of the Great Spirit, they abandoned him on a forgotten piece of land. However, fate would not allow such cruelty to befall a child. An infant Amidaru is soon discovered by a traveling band of orphans and together, they decide to raise him as one of their own, not knowing of the divine calamity taking root within him.
From the day he could speak, Amidaru proved to be a gifted child with unholy power. He possessed inhuman strength, speed, and senses. Above all else, he could control the boundary between the living and the dead; summoning spirits, talking to them, and other odd things. Some of the children feared him and yet, many enjoyed his company. He considered all of them a part of his family and did everything he could to keep them safe. Unfortunately, not everything will go the way one hopes.
One day, a now teenage Amidaru left going off on a hunting trip to acquire food for his family. It normally didn't take him long and he often got by with his rare ability and the katana crafted for him by his adopted brother. However, upon returning to the camp he and his fellow orphans created, everything fell apart. Amidaru's home had been attacked by an army sent by a princess from a faraway land. Everyone had been murdered by the army, every sibling he knew of including his adopted brother.
This sent the young Amidaru into a wild frenzy and through his emotion, the Great Spirit took control. It quickly wiped out the entire vanguard, ripping the souls from their bodies and absorbing their power. Upon taking them in, the Great Spirit noted that humanity had obtained a rather strange power (chakra). Finally, Amidaru calmed to the point of regaining control over his body, only now, he had nothing left to fight for.
Taking up the sword made by his brother, Amidaru became a wandering vagabond. Much of his child-like demeanor had faded, becoming a cold mask. He often took odd jobs, sharpening his skills and earning money for the coming battle. Amidaru intended to find the princess who had sent the army after his family and punish her for such a cruel act. However, he knew that the death of his family was his own fault, with the army being sent to their camp due the rumor of a child who possessed an unnatural power.
And they were right. In the five months after the death of all the orphans, Amidamaru had increased his power exponentially. On top of the spiritual nature of his ability, he now wielded the power of the chakra for a variety of effects and he was only growing stronger with each soul.
A month after traveling, taking odd jobs, and maturing both his shamanic and chakra-related abilities, he finally reached her castle. However, much to his surprise, it was empty. He asked one of the common folk and they told him of a great battle between Kaguya and her sons. In the end, she had been sealed away into the moon and nothing remained. Having once again lost his purpose in life Amidaru fled, hiding deep in the mountains.
Finding no point in remaining how he was, being chased by the world for his power and ability, he decided it was time to move on. During his many months of training and skill sharpening, he'd learn how to freely manipulate his own soul. He could ascend from his mortal body and travel freely and even take control of another. Yes, he would do that. The time of Amidamaru Asakura had come to an end. Now, he would exist throughout time with humanity as his mask and their power as his own.
Amidaru's initial choice came in the form of the Hozuki clan. Not only were they an interesting bunch who enjoyed fighting, they naturally held a fascinating ability. After traveling the astral plane for the better part of a year, Amidaru and the Great Spirit within him came across an infant boy. They could feel the malice festering in his soul and knew exactly what kind of person he would turn out to be. And after letting him grow into adulthood, forcefully took control of his mind and body.
Unbeknownst to any other member of the clan, Amidaru had taken control over their new leader and all the while, his highly potent soul absorbed the other and claimed its power for his own. With this, Amidaru settled for a bit taking the Hozuki clan leaders wife for his own. Not wanting to pass his power on to any other person, he avoided having children at all costs.
During this time, he acquired a sacred sword from the Hozuki that had the ability to manipulate water, as well as absorb ninjutsu and redirect it back at the opponent. With this power in hand, the fame of the Hozuki quickly began to rise and although a once unfamiliar clan, their power had become feared by many. However, Amidaru felt he'd spent too much time on a single person, deciding to move on once again. Upon ascending, the Hozuki clan leader collapsed, dying from the lack of a soul.
White Snake Sage
Amidaru's second vessel took much longer to acquire. Not that there weren't any talented shinobi around him, he just couldn't find any who particularly stood out to him. Soon after he heard the rumor of a nearby cave that contained one of the most powerful clan's in all of history. From what he could tell, they were a barbaric sort with no sanity. What better than to claim the power of madness? And he did. Amidaru traveled to the place they called Ryuchido and found exactly what he was seeking within. Only they weren't mad by nature, the rush of power they wielded ultimately sent them into a fit of insanity.
It seemed like their bodies were capable of passively absorbing the natural energy from the atmosphere. Amidaru had heard of this and believed this to be the power he sought. By taking control of one of the clan members, he sealed away his mind and thus the ability to go mad. However, he found handling such a power to be quite easy and enjoyed it. In fact, he ended up leaving the back of the cave and going off to find another interest relating to Ryuchido, the White Snake Sage. the Sage took an immediate interest in a member of the clan who could apparently control their power, unable to sense Amidaru's presence within him.
Amidaru asked if he were willing to teach him how to invoke the ability known as Sage Mode. The White Snake Sage agreed, if Amidaru could withstand his bite. Without any hesitation, The White Snake Sage erupted from his perch sinking its fangs into Amidaru's neck, injecting him with senjutsu. After an hour of torment where he thought he might lose his own sanity, he finally overcame the trial and was mentored in the art of Sage Mode.
Taking control of a third vessel took very little time and effort. In fact, it came to him right after the founding of the villages. When Iwagakure came to power with its mighty military strength, Amidaru couldn't help but become interested. Upon his arrival, he met a man of tall stature who bore the title of Tsuchikage and according to those who worked for him, possessed an ability none of the other Kage did. Intrigued by this fact, Amidaru took control of the man and fed on his soul to obtain an ability called Kekkei Tōta.
Upon claiming the soul of the Tsuchikage, he decided to use the power entitled to him to access all of the villages research in order to unveil a possible future candidate. Unfortunately, it bore no fruit and without any purpose to stay in his current body, he moved on leaving his host collapsed in his office.
Amidaru's fourth life came in the form of a nearly extinct clan. They were long forgotten by history and only a few remained. After searching the astral plane for two years, Amidaru was finally able to catch wind of where they were hiding. He quickly confronted the group and confirmed their talent. Unlike any other clan he'd seen before them, these people had the power to manipulate the raw power of weather.
They could summon rain, lightning, and fierce winds on a whim. Deciding that they were worthy of being one of his hosts, he claimed the soul of one of six remaining members and remained among them to master the fierce power they commanded. It took him about a month to completely understand their bond with nature and how it remained a link to their emotion state. By bringing forth anger, he could summon lightning from the sky.
By bringing forth sadness, he could create rain. There were many possibilities with such an ability. Unfortunately, Amidaru didn't want to linger any longer than necessary and moved on after several months of practicing.
Having collected a fair bit of strength, Amidaru felt he could only go one step further. He intended to open a gate to the Pure Land. In order for him to bring forth a gate, however, he needed to come to terms with the divine calamity within. Like any other time when he wanted to speak to the Great Spirit, he meditated. Only now, Amidaru had returned to the mountains where he had once left behind his original body. Upon entering the inner world of the Great Spirit, he asked the entity what it would take for them to work together. Much to his surprise, the Great Spirit simply told him that if he could willingly accept the death of his family, he would allow Amidaru to fully synchronize with its power.
Knowing of no other way to complete the task at hand, Amidaru agreed. And then, everything changed. A column of blinding light fell from the sky, striking the very essence of his immortal soul. When the light faded from the world, Amidaru had regained his original body and yet, retained all of the power he'd collected over time. With their bond complete and the full power of the divine entity at hand, he opened a path directly into the Pure Land.
Upon his entering, he found it to be nothing like he expected. A room full of light and those who had departed long ago. However, Amidaru had come to the afterlife for only two people. Both of which he could tell were not far off. With this in mind, he delved deeper into the spirit realm. About an hour into his search he found them, the two who would bring about the end of his plan. Indra and Asura Ōtsutsuki. The grandchildren of Kaguya Ōtsutsuki.
The irony of such a situation made Amidaru smirk, a sign of victory. Kaguya had murdered his family and now, he claimed the power of hers. Utilizing the power of the Great Spirit, he assimilated both of their souls into his very being. With the power of Indra and Asura fully united within him, something terrible occurred. A third eye awakened in the center of his forehead in the form of the Rinnegan, only it contained the tomoe produced by the Sharingan; a union of both bloodlines in a single eye.
However, it lacked the unique abilities wielded by Kaguya's Rinne Sharingan. With Indra and Asura's power overflowing within him, he departed from the Pure Land.