Buddhist fairy tales ala SGI style!

I have been wondering where fairy tales from SGI come from like buddha nature, human revolution, poison to medicine, etc. as I cannot find these in any of the sutras preached by the original buddha Siddhartha Gautama? One key reason why I left the SGI besides the constant Ikeda worship and lack of buddhist study was the loss of focus on real buddhism. Also the magic chant is a dud.