Originally Posted by Rokudaime Sennin ™
The true invincible GOD of NarutoVerse. All of Rikudou's weapons/jutsus were most likely done with onmyoton and yinton/yohton (yin/yang) releases.
Sword of Totskano - it's a spiritual sword that affects the souls, would be a yin release.
Yata's mirror - shield that reflects all attacks, spiritual or physical, so onmyoton release maybe?
Susanoo itself is an onmyoton release for sure.
Amaterasu = yang
Tsukuyomi = yin
Izanagi/Izanami = Onmyoton
Soul sealing Gourd - onmyoton as well as it's a physical object that seals souls.
I think Rikudou left all this stuff in order to ensure that his descendants would have the proper tools to take care of the bijuus. His sons were supposed to have worked in harmony to protect the future until their feud messed up Rikudou's plans. Rikudou's Amaterasu would've turned black due to the elder son's hatred/going to hell.
Oh and poor Samui's soul got sealed cause she thought of the word, LOL.