Strider Hiryu Gaiden (ストライダー飛竜外伝) is a special chapter of the original manga released in the December 1988 manga anthology Monthly Comic Comp. Since it was released after the manga finished its serialization, this chapter was not included in the collected edition and was never reprinted, making it extremely rare to find.
The chapter's story reveals Hiryu's state of mind after having killed his sister Mariya and the effect it had on his ability as a Strider, and focus in his final mission before he retired from the Striders.
The chapter is set half a year after Hiryu was forced to kill his sister Mariya. Ever since that event, he has become much more erratic, aggressive and reckless during missions. Carrying the burden of Mariya's murder, Hiryu himself has lost the will to live, and continues fighting simply as a demon of destruction who seeks his own death in battle.
As the chapter begins, Hiryu is traveling through a blizzard as he recaps his assignment: he must rescue Dr. J. Hogan, the world authority in nuclear fusion, who was kidnapped a month ago by a terrorist group calling themselves the "Phantom Unit", who demand the release of one of his captured members in exchange of the doctor's life. Hiryu has a time limit of 3 days to rescue Hogan and exterminate the terrorists.
While Hiryu carries out his mission, Kain confronts Kuramoto back at the Striders' HQ over his decision on sending Hiryu alone, calling him on wilfully ignoring his current state of mind or the fact he's probably seeking a way to die. Kuramoto, rather coldly, tells him that Hiryu is no novice agent and has been given a mission, and that the organization has no need for "emotional Striders" who drag around traumas from the past. Wile this leaves Kain shocked, in truth Kuramoto has sent Hiryu on this dangerous mission confident that, if he survives the ordeal, he will overcome his grief.Meanwhile, Hiryu confronts the leaders of the Phantom Unit, the sibling duo known as the Zangi Brothers. A fierce battle ensues, with the brothers (said to be equal in skill to an A Class Strider) proving to be cunning adversaries, gravely injuring Hiryu's left arm and even shooting him in the chest. Still determined to finish his enemies at all cost, Hiryu pushes forward and finally terminates both brothers. Upon checking his chest wound, however, he finds out the bullet was stopped by a pendant he was wearing which once belonged to his sister. Realizing that his sister wouldn't want him to die this way, he decides to continue living fully in her memory.
In the chapter's epilogue, Kain sees Kuramoto again, now having realized the old man's true intentions: as Hiryu is no longer fit to be a Strider, and a Strider's path irrevocably ends in death, Kuramoto has given Hiryu a chance for a "special retirement" after the end of the mission. Kuramoto simply responds that, as far as they know, "Strider Hiryu" is dead. The final panel shows Hiryu, bandaged but smiling, riding a horse as he observes a vast prairie...