The (normal modern day high school girl) protagonist is suddenly wrapped up in an incident and is thrown back in time to the Warring States period. There she meets Uesugi Masatora (later known as Uesugi Kenshin). Masatora is interested by the fact that she comes from the future, and so he invites her to the castle as an "Envoy of Bishamonten". There she begins to be protected by a group of ninjas called "Nokisaru".
correct dump!
Other games in the series