The Dragon Lineage was an ancient race that fought and sealed the evil deities. Later known as the Hayabusa clan of ninjas, they were charged with protecting two legendary weapons: the Dragon sword, a sword that has been passed down from generation to generation in the Dragon Lineage and entrusted to young Ryu Hayabusa while his father trained in the wilderness, and the evil Dark Dragon Blade, a sword made from the bones of an evil black dragon & the dragon's evil power sealed within so none may use it.

The Dark Dragon Blade was guarded in the Hayabusa village. The village was abruptly attacked by forces of the Vigoor empire, a force led by a Greater Fiend named Doku; Ryu was away visiting the master of the Shadow clan, the nunchuku master Murai who is also his uncle, in his fortress. Doku slaughters all who stand in his way, defeating Ryu as well, and departs with the Dark Dragon Blade. During Ryu's convalescence, Murai's espionage network learns that Doku is responsible for the theft, but he had stolen it at the behest of the Vigoor emperor; they aid Ryu in infiltrating the secretive Vigoor empire to retrieve the cursed blade.

The only available transportation is a zeppelin; it is swarming with Vigoor special forces, who know of Ryu's presence. The ensuing battle destroys the zeppelin, and Ryu lands near the capital. Atop one of the city's nightclubs, he meets Rachel, a beautiful and scantily-clad Fiend Hunter. She warns Ryu about the dangers of fighting Doku. She then uses her hookshot to swing back into the city to fight Fiends. Ryu then encounters a mysterious man with round shades and a top hat, who introduces himself as Gamov. He appears to know a lot about Rachel. Before Ryu can say anything to him, he leans over the ledge of the building, and mysteriously disappears. Investigating with the help of Murai's spy, Ayane, Ryu learns that he can enter the palace through a underground path accessible via an old monastery. There Ryu meets the fiend hunter Rachel again.

After defeating a large tentacled fiend known as Hydracubus and saving Rachel's life, Ryu leaves Rachel with Ayane and enters the monastery. He makes his way down into an underground graveyard, and from there finds another path that could lead to the palace of Zarkhan. However, an unfortunate incident occurs and the underground area floods with water, forcing Ryu back to the monastery. There he meets Alma. Alma used to be Rachel's sister, but they carry a bloodcurse which renders them susceptible to twisting by evil fiends; this twisting is how a Greater Fiend is created (as opposed to Lesser Fiends which are brute unthinking monsters, Greater Fiends are considerably more powerful and retain their intelligence). Alma was captured by Doku and so twisted. The reason Rachel is a fiend hunter is to liberate her sister through death and to encompass revenge on Doku.

The aftermath of the explosive battle damages the monastery, which causes the Vigoor army to deploy forces in the capital. Ryu traverses the city filled with soldiers and army vehicles to the military supply base on the outskirts. Once there he destroys the radio communications tower, escaping on a stolen train found on a turntable, which Ryu crashes into another train to cover his tracks and mislead the army.

At the crash site Ryu finds a new way to get into Zarkhan; through the underground aquaduct. It leads him to the Moat of Zarkhan, but not before he slays the Fiend Paz Zuu. Swimming through the moat, he finds his way back into the Hidden Underground and subsequently the Monastery. There he takes a now-operational elevator to the Zarkhan Stadium, where he battles Doku once more and this time comes out victorious. The body of the fallen Lord of Greater Fiends disappears in a manner similar to Obi-Wan Kenobi's death.

The other exit of the Zarkhan Stadium leads to the Palace of Zarkhan, but the doors are locked. Ryu heads into the Caverns, the only other unexplored area, and picks up

Ryu has the demeanor and wisdom of a man far older than himself, due to his prolific lineage and mantle of station as a respected ninja. His exploits have given him an attitude far removed from most others, and he understands things in more abstract and philosophical terms. Much like Gen Fu and Eliot, he adopts a tranquil nature, much akin to water; free flowing most of the time, but unforgiving and crushing when roused. Through the Dead or Alive tournament, he has extricated himself from many of the subplots involving other characters, concentrating instead purely on the larger goals that present themselves.

He is Hayate's best friend and an ally of Kasumi and Ayane. He and his ninja brethren have been direct players in the defeat of every major threat in the D.O.A. tournaments, himself defeating the rogue Tengu in single combat during the second tournament. Ryu has befriended several people from the DOA tournaments, notably Jann Lee, with whom he shares a mutual respect.

In Ninja Gaiden, Ryu is acquainted with female protagonists like Rachel and Irene. On the other hand, Ryu has been betrayed by some of his allies such as Foster (NG III: The Ancient Ship of Doom) and Murai (NG Xbox).