Ryu first appeared in the Ninja Gaiden beat 'em up arcade game in 1988. In that same year, Ninja Gaiden was released on the NES (Famicom, in Japan) and the Sega Master System, though these versions, being more centered around platformer-style gameplay, bore little resemblance to the original arcade game. Two NES sequels, Ninja Gaiden II: The Dark Sword of Chaos and Ninja Gaiden III: The Ancient Ship of Doom, followed in 1990 and 1991 to complete the trilogy. Also in 1991, Ninja Gaiden Shadow was released on the Game Boy. Ryu's next few appearances were as a playable fighter in the Dead or...
Ayane was born as the result of Raidou raping Kasumi's mother, Ayame. Though Ayane was allowed to stay in the ninja clan, she was always looked down upon as a "poisoned child", generally ignored by many of the ninja clan. Ever since they were children, Ayane admired Hayate. She looked up to him as a way of increasing her self-esteem and lifting her sadness. Hayate as well was fond of Ayane; he might have learned of the true circumstances behind Ayane's birth and did not see the point of isolating her as everyone else did.