Ninpiden
The Ninpiden is an authentic ninjutsu manual written by Hattori Hanzō in 1560. It is regarded as one of the three key historical texts of ninjutsu, along with the Shōninki and the Bansenshukai. It was passed down in the Hattori family, and was considered a secret transmission; it was not shared with outsiders and even within the family, few had access to it.