Who cares about their origins. We all think of them as damn sweet and intimidating.
Thats all that matters

Hanzo Hattori’s post about it being derived from Shugendo is true. I studied with the Yamabushi and both Tenkawa Mura and Hargurosan doing research on Buddhism and Japanese religion, since Omine Shugendo has its roots in Shingon. The armies of Omine and Hagurosan evolved into what we now know as Ninja when Nobunaga called on these armies in his attempts to unite all of Japan. This is actually why he invented the nightingale floorboard so that he wouldn’t be assassinated by the very people he used to obtain power.

I would like to correct one fact on Hanzo Hattori’s post and that is the they where not unnecessarily a low caste. Many if not most where just common farmers, until Nobunaga started calling for them, at this point class mobility amongst these mountain warriors sky-rocketed. This allowed some to gain great power and become Samurai.

Also since they are followers of Shugendo they grew up learning about the mountain ascetic arts. This is where Ninja Magic comes from, the idea of overcoming gravity, vanishing and all of these mystic arts are still practiced and part of the initiation ritual into Shugendo.

This post is so very wrong, that is almost boggles the mind. The poster wither did little research, nor non what so ever, and using Wikipedia is not a reliable source of information.