Through the Blades of Grass in the Field of Kusa Fly...Shuriken

Shuriken, a weapon of the ninja that people know so well. Or so they think.

Shuriken are portrayed as great throwing weapons utilized by the shinobi in many media aspects of Japanese culture. They originated from tools just like many other weapons any any culture, but just as any weapon they had their purpose.

My main question; What were some of the origins of all the different variations of the Shuriken floating around throughout history?

Do you think you can fill in some of the blanks in The Field of Kusa???

Yatagarasu （やたがらす）

Yatagarasu, the three legged raven of Japanese folklore. Many people know of it, but it also holds history of the shinobi within it. Yatagarasu can be seen as one of the 1st shinobi symbols in history, where he was recorded to have flown down to help Emperor Jinmu in his time of need as a guide to help him travel from Kumano to Yoshino. On his trip he was encountered, and from the sky came a blinding light in the shape of a kite that took place upon his bow and blinded his enemies, and led to his victory and eventual titling as Emperor. 

Yatagarasu was also a symbol said to be sent from the Sun Godess Amaterasu （あまてらす）and the interesting fact that connects Yatagarasu to the arrival of a blinding light from the skies, to me links those two together well. 

There is also the fact that Yatagarasu is a raven which is a highly intelligent animal and very similar to that of the Tengu. Tengu were said to have given rise to the ninja. 

There is much interconnection, tell me can you add on to it and help brighten the light in this field of Kusa?