"Different evolution of Byakugan due to mutation helps in understanding the elements in a better way. But natural evolution is difficult. It requires us to have basic mastery of any one of the 7 elements. So it is mainly time consuming. Most of our clansmen depend upon mutation for their evolution. Then they learn about element according to the mutation. So many of our clansmen choose to eat chakra fruits as it helped them in mutation. Sometimes more advanced evolution occurs due to chakra fruits where they gain shortcut to master over more than one element."
"So, after discovering this effect our clansmen greedily start to collect chakra fruits which lead to this situation. Ren, I know this way of gaining power is tempting, but you have to bear with it. It's not the correct way. For our power, we destroyed many planets and many lifeforms were drove to extinctions."
Ren can understand his mother's concerns. He knows that humans, if given chance, most of them will do the same to gain power. So the less people know, the better.
"Okay, now I have told you about evolution due to single element. But this is just the beginning. The more you master elements, the more powerful the evolution is. Then comes combining of two or more than two elements (kekkei genkai, kekkei tota etc). The most powerful evolution is Rinnegan also known as 'Samsara Eyes' when someone has basic mastery of 'Yin-Yang'. It allows user to transcend the border of life and death. It can be said that you have just touch the doorway to immortality. Some clansmen open these eyes under strong emotional fluctuation. But they don't gain full power of Rinnegan. They just gain some abilities and mastery over elements become easier for them. Without training or proper guidance, it waste the potential of Rinnegan."
Ren knows about Rinnegan prowess as the anime series was mostly based on Rinnegan. But except for Sage of Six Paths, no one did proper utilisation of Rinnegan. Like 'Creation of All Things', Hagoromo use that technique to give life to Tailed Beast. Ren thought that, even Hagoromo didn't properly master the power of Rinnegan as he spent most of his time spreading Ninshu.
Ren started thinking, "Maybe, both Hagoromo and Hamura were alive but the anime didn't show it. The anime was mainly focused on Naruto and Sasuke, their struggle and friendship. To allow them to be center of attention, Hagoromo and Hamura were shown dead and were shown in their spirit form. Or maybe they were weakened when they started Ninshu culture. Mother was weakened severely when she revived as she didn't get all the spread chakra. Otherwise, Naruto and Sasuke would have no chance to seal her. It was stated that Hagoromo and Hamura fought against mother for months where land broke apart, ocean dried. They only managed to seal her with great difficulty and mother was also hesitant to use her full power against them. After all she loved them both. Moreover, from what I know now about mother, she has no combat experience. Father mainly fought, while mother spent time hiding from pursuers. If someone like Madara got mothers power, then the result would have been different. It seems that I cannot depend upon my previous knowledge to judge someone's full power. If I underestimate them, I will suffer."
Kaguya watched her son deep in thought, she was happy. She knows that beside giving the knowledge of their bloodline she can't give him anything in her current situation. She thought "Ren, forgive mother for not giving you anything other than knowledge. Hope that this will help you in the future." After giving some time to Ren to digest what she told, she continued her explanation.
"Ren, if you awakened Rinnegan someday, don't get too excited. Try to use them to achieve mastery over 'Yin-Yang', then you will know the true power of Rinnegan. If you depend upon self-awakened abilities of Rinnegan, you may never reach the true height of powerhouse like your father."
"I know mother, I will keep your words in my mind."
"Good son. Because Rinnegan is not the final evolution of our bloodline. Your father had awakened the eye which is the speciality of our ancestors. The eye which make our clan famous. The eye which truly belongs to Lord Shiva. His third eye known as Rinne Sharingan. Known as 'Saṃsāra Copy Wheel Eye'. The nine tomoes which represent the 7 elements and space-time."
Ren gasped when he heard her mother described about Rinne Sharingan. Not much is shown about their capabilities in the anime. That doesn't mean they are weak, but rather no one knows the true power of Rinne Sharingan. Madara used it to cast 'Infinite Tsukuyomi'. But that is self awakened power. If given time, many abilities could have been awakened later. His mother used it to cross dimensions and forcefully brought other into them. From this you can imagine how overpowered is Rinne Sharingan. Truly worthy to be known as 'Eye of Destruction' of Lord Shiva. He didn't know, how much his father has gain from that eye.
"Rinne Sharingan is most difficult to awaken. Your father only awakened in a life and death situation during battle. Although he didn't have time to fully realise its capabilities, from what I have heard from him is that it is very powerful. So much that you forget your own personality and awake a God complexity. He was almost drown in the power, he barely managed to overcome it. He warned me that, if awakened Rinne Sharingan, the less you use the better. Otherwise you will become a puppet who only knows to despise others for their inferiority. Best not to use them if don't have to. Individuals with weaker willpower will be driven mad, become a Shura, who only knows madness and destruction."
Ren can now understand why his become like that in the original. He promised himself to save his mother from that tragic fate. He doesn't want to lose his mother. He asked his mother
"Mother, how can we awaken Rinne Sharingan?"
"Well to awaken it, you first have to have a pure bloodline. By training, you can awaken them during special circumstances. Not much is known about it. From what I know, your father maybe the only one who has awaken it except for our ancestors. Nobody knows it's true power. From what I have seen in case of your father, it looked like Rinnegan with 9 tomoes and red background with 3 black concentric circles. If you ever awaken them, I advise you to first explore it's capabilities before using."
"I will keep in mind mother."