Gaiden
This OAV series came out the summer after the TV series ended. The timeline puts it around mid-August of 1989.
New characters: Luna, Uncle Chin, Shikaisen, and Mad Scientist.
Again the Armor Soldiers!
Nighttime in New York and Halo stumbles upon a gang. They tease him for a bit and then proceed to attack him. Ignoring their attacks, Halo picks up two guys by their heads and crushes them. Halo turns to a guy with cropped hair and a tank top and his girlfriend. Screams are heard in the alley and dogs howl. Halo stumbles on but a strange mist pours out of it. The empty armor floats off of the ground and the mist coalesces into a short old man with a putty head.
It's Ryo's sixteenth birthday and his friends are throwing him a party in a hotel in Shinjuku. Everyone is there but Sage, who is on a trip in New York City. Halfway through the party, Ryo catches a news flash about a mysterious green armor wanted for killings in New York City. For a moment, the Halo's emblem is flashed across the scene. Mia also catches the end of the report.
Several days later, Ryo is on a plane to New York and is surprised by the presence of Kento and Sai on board. Sai tells him that Mia figured Ryo would do this and that she, Rowen, and Yuli are already investigating in New York. Mia, Rowen, and Yuli ask a reporter in the Times building about the photographer who took photos of the green armor. Around the corner, a girl eyes them warily. The plane that Ryo and company are on is attacked by a strange apparition as the plane enters New York City air space. This ghost, cutting off the part of the plane's tail, forces the plane to land in the harbor.
Meanwhile, Rowen has tracked down the photographer only to find that he has been murdered. Then Rowen pulls out the knife from the man's chest. Conveniently, the girl from the Times building followed Rowen here and saw him with the knife over the dead man. She runs off crying murder with Rowen right behind but Rowen loses her on street level. The girl is shown hiding in the shadows with an angry look.
That night, Mia and company discuss their investigations at Kento's uncle's restaurant. Mia had gone to Columbia University where Sage had supposedly been invited to attend an exhibition or lecture on Japanese blades. Uncle Chin welcomes them to New York and offers to let them stay at the restaurant when Nasuit tells him they haven't found a place to stay. Then Ryo, Kento and Sai show up. Kento scolds his uncle for being so familiar with Mia. Then waitresses run screaming from the kitchen as that girl runs out crying revenge and tries to stab Rowen with her knife. It's Ryo who stops her but she runs off before anyone could question her. Kento wants to chase her but Ryo stops him since she probably has nothing to do with them. Rowen mutters that she already considers them an enemy.
The girl is shown running through the old subway, asking forgiveness from her older brother for not being able to avenge him. In her room where she is brushing her hair, she picks up a photo of her and her brother and starts to cry. The man in the picture is the same one who flicked out a knife to try and stop the possessed Halo armor in the beginning.
Somewhere, Sage is experiencing nightmares. It is through these nightmares that Sage's Halo armor is being manipulated. Sage's pain reaches Ryo's mind and wakes him up in the room that he's sharing with Sai. Kento and Rowen are eating hamburgers at a fast food joint when they hear a commotion outside. The Halo armor is attacking the town again and Kento and Rowen armor up to challenge it. That's when they see that Sage isn't in the armor. Even as they're fighting, a crowd watches and cheers. Kento asks what are those idiots doing and why don't they get away. Among the crowd is the mysterious girl. The battle stretches into the night and the NYPD and the army are called in.
Ryo and Sai catch the news report and immediately run to the battleground. By the time they get there, Kento and Rowen have been severely beaten, Rowen especially, he can barely get up. The Ronins know they have to get away as the helicopters begin firing on them. The Halo armor also escapes but not before Shikaisen reveals himself to the Ronins. Running from the soldiers and police officiers, Ryo and Rowen separate from Kento and Sai to evade their pursuers. Hiding in an alley, Ryo and Rowen are confronted by the mysterious girl who offers to lead them to safety.
Save our friend, Samurai Heart
Running through the subway, the three escape the police. By now, Rowen and Ryo have returned to their civilian clothes. The girl leads them farther down, somewhere beneath the subway. They thank her for helping them and she tells them her name, Luna, and why she's been following them. Luna also surprises them when she bandages Rowen's injuries. When Kento and Sai arrive, Kento challenges Luna before Ryo can get a word in. Kento looks very confused after Ryo explains that she is not their enemy.
Meanwhile, Uncle Chin's restaurant is attacked by Shikaisen's ninjas who kidnap Mia and Yuli. They leave a message behind telling the Ronins to come to Japantown. At that time, a festival is interrupted and destroyed in Little Tokyo in Los Angeles. Mia and Yuli are tied up and forced to witness the deaths of all the festival goers.
When they return to the wrecked restaurant, the Ronins swear to answer Shikaisen's challenge. They decide that after Rowen has recovered, they'll go after Shikaisen. That evening, Luna talks with Ryo on a bridge and convinces him to let her come along to Los Angeles.
The next day, all six of them are walking through the ruins of the festival. Using the armor spheres, they're drawn to a cemetery where they are attacked by Shikaisen's ninjas. The Ronins easily defeat the ninjas. There is a priceless scene when Kento saves Luna from one of the ninjas but she's too busy cheering on Ryo to notice. The remaining ninjas run away into a temple where the Ronins and Luna are confronted by Shikaisen. He draws them through a trapdoor into his headquarters.
Everyone but Luna falls into the water surrounding the center stage where the computer and Sage are located. The mad scientist greets them and activates a beam that electocutes the Ronins. Mia and Yuli swing on their rope to knock the scientist away from the console. Immediately the Ronins free Mia, Yuli and Sage.
When Shikaisen appears again, Sage dons his armor and attacks him. But Shikaisen activates the computer and the five warriors are trapped in his magical seals. The mad scientist, holding Mia off by gunpoint, is analyzing the data from the other Ronins and doesn't notice Yuli pulling himself up from the side. Unfortunately, Shikaisen sees him and would have killed him if Luna didn't jump in from the side trying to avenge her brother.
Shikaisen easily knocks her away. Yuli used that moment to distract the scientist so Mia can deactivate the seals. Ryo breaks out of his and rushes to Luna. She tries to say something but dies without saying a sound.
The Ronins then armor up to defeat Shikaisen. Ryo fights him alone and blasts Shikaisen with his So En Zan. But Shikaisen's remains merge with the computer and the scientist, creating a visual projection of Talpa. Having analyzed all their armor, the computer easily counters their attacks. They call on the Inferno which the computer hasn't analyzed yet and therefore can't counter to destroy it. Back in New York, on the same bridge that Luna convinced Ryo to let her tag along, the Ronins throw flowers in Luna's memory.
