Take 3 pounds of fresh Ninja Gaiden Black (or Onimusha 3 if Ninja are out of season), a 20 oz box of actual historical events and entities, moisten with a cup of Dark Souls, mix well, and bake in a 1600 AD oven of Japanese Warring States.

Hideyoshi is dead. Who will be the next Shogun? Well, these Movers & Shakers - some toying with demonic and undead forces - may well have the last word. Unless, perhaps...YOU would like to speak up?

The details are astounding. Historical, mythological, equipment, architecture, decoration, even down to the sword drawing animations.

*BONUS*: I can free run and side slash an opponent in passing with my (N)Odachi in Mid-Stance a la Bushido Blade.
Pro-tip: anything I can compare favorably to Bushido Blade is something amazing, whether game, film, book, or idea.

You should all read Taiko (about Hideyoshi) and Musashi, both excellent novels by Eiji Yoshikawa. Also the Sano Ichiro series by Laura Joh Rowland, about The Royal Investigator Of People, Places, and Events.
The Tomoe Gozen series by Jessica Amanda Salmonson offers a more fantastical/mythological angle which fits in really well with Nioh's setting.