kaguya probably split her power between hagaromo and other son .This could explain why hagaromo split his powers to his sons indra and ashura.Hagaromo know about his mother power lust in the past and realise his only method to stop her by combining his powers with his brother to become complete.Let say hagaromo originally have yang chakra and his brother had yin chakra and they fuse to gain the third eyes like kaguya.The complete sage of sixth path (hagaromo + his brother) defeated her mother with a jutsu that make her become a death reaper demon as her punishment.
Similarly ,I believe Naruto and Sasuke will fight current Madara together but separately .Madara will eventually seek the god fruit to get more power ,this will push Sasuke and Naruto fuse using the sage staff as a medium .The sage staff have it yin and yang form and it combine form,Sasuke and Naruto both represent these form.What your taught
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Similarly ,I believe Naruto and Sasuke will fight current Madara together but separately .Madara will eventually seek the god fruit to get more power ,this will push Sasuke and Naruto fuse using the sage staff as a medium .The sage staff have it yin and yang form and it combine form,Sasuke and Naruto both represent these form.What your taught