Ryu Hayabusa - he is main protagonist and playable character in Ninja Gaiden series and debut in original of Ninja Ryukenden in 1988. He is son Jo Hayabusa and nephew of Murai.
Irene Lew - also as Irene Liu and Aileen por spelling, she is main female character in original of Ninja Ryukenden series and she is an agent of the CIA's Secret Auxiliary Unit, working under the codename "Sea Swallow".
Ayane - she is female character in Dead or Alive series, debut in DoA1 (PS1 version). She called Hayabusa is "Master Ryu" in order to respect to him and his rank and she is playable in Ninja Gaiden Sigma...