Hello, I am new here! This is my first post !
My theory is about the Sage of the Six Paths having Sage Mode and leaving the Sage Mode to The Younger Son !
The name of the Sage of the Six Paths its still unknown... I belive people where caling him " The Sage of the Six Paths " because he could use two powerful things !
The Six Paths !
The Sage Mode !
The names of this jutsus gives the name " The Sage of the Six Paths "
The Sage of the Six Paths ( Rikudō Sennin )
The Six Paths = Rikudō
Sage Mode = Sennin Mōdo
I belive that the Sage of the Six Paths left The Sage Mode to his Younger Son !
The chakra around him looks like a person having Natural Energy around him !
I dont know why the Younger Son didn't say something about Sage Mode to his Clan or maybe he did but somehow it was lost and the Sage Mode was keept only in the sacred places...Mount Myōboku...Ryūchi Cave...Shikkotsu Forest