Ninja Blade has players taking up the mantle of a modern-day ninja named Ken Ogawa, defending Tokyo from horrible mutated monsters formed from parasite called "Alpha Worms". The producers aim to make the transition from gameplay to quick time event back to gameplay seamless.
From Software producer Masanori Takeuchi has said that he anticipates the game to be around 12 hours long. The cityscape of the game is realistically modeled around Tokyo, so Japanese gamers can visit a few similar locales during the course of the game.
In July of 2011, a group of United Nations peacekeepers encountered a small pack of mutated carnivores in a Northern African village. Further studies of these animals (and their victims) show that they have Alpha-worms, parasites that turn its hosts into grotesque and violent monsters. Fearful of these new biological threats, the UN destroyed the research site holding them. It also created the G.U.I.D.E task force in response to more Alpha-worm sightings in other parts of the world. This elite squad consists of highly trained ninjas led by their master, Kanbé Ogawa.
On August of 2015, G.U.I.D.E traveled to Tokyo to deal with the Alpha-worm presence there. The parasites multiplied rapidly in the Japanese capital and spawned many mutants of unprecedented size and danger. Ken Ogawa, a G.U.I.D.E ninja who is also Kanbé's son, defeats a Pox Giant and subdues a large armored Arachne. But before the task force can deliver the killing blow to the latter, Ken's rival Kuroh begins attacking his ninja colleagues. He and Kanbé are under the control of the Alpha-worms, and they kill most of the G.U.I.D.E squad; only Ken survives the onslaught. With its task force all but gone, the United Nations suggests firing an orbital laser on Tokyo as a means to permanently wipe out the Alpha-worm infestation. But Agent Michael Wilson, the G.U.I.D.E head and its liaison with the UN, successfully convinces his superiors to postpone the use of the superweapon. He thinks that the recovered Ken Ogawa can single-handedly rescue Tokyo from the parasites and prevent further harm towards the city's uninfected citizens.
Ken rewards Agent Wilson's faith in him by defeating a variety of dangerous mutations. After a string of victories the ninja confronts Kuroh, who invaded G.U.I.D.E's Tokyo headquarters and held its occupants (like Wilson) hostage. From the intense battle with his rival, Ken learns that he is merely a genetic clone of Kanbé Ogawa. That is, he is a living weapon designed to destroy the parasites, and that he inherited the ninja master's immunity to the Alpha-worms. After Kuroh's defeat, Kanbé reappears in front of his son while fighting off the parasites' influence. He admits to forsaking his immunity as a ploy to discover his hosts' nerve center. If Ken finds and destroys that area of operations, the Alpha-worm threat is over.
Father and son meet again at Tokyo Tower for a showdown. This time, the former is under the Alpha-worms' control. Kanbé initially gets the upper hand in the battle by unleashing the powers granted to him by the parasites. But Ken turns the tide by unlocking and unleashing the Ninja Blade, a powerful weapon that feeds on the life force of its user. The swordfight abruptly ends when the Hive Core of the Alpha-worms fuses itself with Kanbé's body, resulting in an enlarged and mutated form of the ninja master. But despite this intervention from the parasites, Ken still manages to best his father by jumping into his mouth and deliver a finishing blow to the Hive Core inside. And without the Core to sustain itself, the Alpha-worms slowly die off and disintegrate.
Despite a momentous victory, Agent Wilson still fears for the Alpha-worms' return. He needs to rebuild the G.U.I.D.E task force with capable warriors who can fight the parasites when that time comes. But until then, he tells Ken Ogawa to remain vigilant. That ninja is the only person alive with the expertise and experience necessary to beat back those mutants.
The gameplay in Ninja Blade consists of boss fights, platforming, and quick time events. When you're not fighting a gigantic boss or mashing on the face buttons in a QTE you're left with an adventure action game comparable to Ninja Gaiden or God of War. There are four weapons in the game a heavy sword, a katana, twin blades, and a large shuriken. The katana is your main weapon. It is the middle ground between the powerful but slow heavy sword, and the weak but fast twin blades. The heavy sword is used to break through walls and destroy enemy armor and shields. The twin blades are used as grappling hooks and have a variety of useful area attacks. In addition to the three main weapon you have a shuriken that you throw to use your ninjutsu. There are three ninjutsus: wind, fire, and lightning. All of these can be used to effect the environment along with attacking enemies. Every weapon and ninjutsu can be upgraded four times by collecting blood crystals that fall out of enemies.
Ninja Blade features a considerable number of bosses, most of which are depicted as gigantic mutated insects, slimes etc.The boss battles involve numerous quick time events and - in most cases - it takes several phases to beat the boss. The boss finishers can be characterised by a large dose of acrobatics, violence and over the top nonsense. When the bosses' life meter reaches zero Ken is able to initiate the finishing sequence called todome. The bosses include:
- Pox Giant
- Impaler Leech
- Scolex Worm
- Slime Chopper
- Plague Snail
- Carrion Claw
- Tojiro Kurokawa
- Ryoko Kurokawa
- Fire Hydra
- Blast Mite
- Stalker Larva
- Mylasia Fly
- Mutant Andy
- Kuroh Sakamoto
- Phlox Arachne
- Kanbe Ogawa
- Mutant Kanbe