the series originated in 1997, with yoshiki okamoto's idea to create "sengoku biohazard", a ninja version of capcom's own 1996 "resident evil" (known as "biohazard" in japan), set in the sengoku period and featuring a "ninja house" filled with booby traps, similar to the mansion from "resident evil", where battles would be fought using swords and shuriken: "the house will contain hidden doors behind walls, ceilings that fall down to you, scrolls and ninja magic, and many other ninja techniques." the project was originally intended for the nintendo 64's 64dd.