We see the opening flashback through young Ryo Takatsuki's eyes. A strange voice asks him if he wants power. Ryo has been crushed in a building collapse. As the doctors work on him he hears the list of his injuries, especially the fact they can't save his right arm. Growing weaker, he wonders if he is dying. Desperate, he screams he is not ready to go yet. The voice accepts. Cut to the present day, the modern–day Aisora City, part of greater Tokyo. We see a typical Japanese high school, a couple of multi-storied buildings surrounded by athletic fields. And rappelling down the side of one of those buildings is 17-year-old Ryo, who is looking at some swifts nesting on the side of the building. Down below, Ryo's irritated girlfriend, Katsumi Akagi, demands he come down immediately! Ryo complies with good humor, and they and other students start cleaning up the grounds. Suddenly Ryo badly cuts his hand on some glass. His shocked classmates see the cut heal almost instantly. Ry

The boss holds Katsumi hostage, and introduces himself as Claw. He demonstrates his name by popping several nasty claws out of his cyborg hand. Claw knows Hayato, who has already killed five of Claw's fellow agents. But of course he's not normal, he's an ARMS just like Ryo, one who has an arm of immense power. Hayato is stunned: Ryo's not an enemy? Ryo doesn't care, he just wants Claw to release Katsumi. Claw says if they surrender, he won't kill them . . . maybe. Katsumi suddenly breaks free and runs towards Ryo, but Claw strikes at her from behind. Ryo can't get to her in time! Suddenly Hayato is there, grabbing Claw's arm with his own mutated limb and protecting Katsumi. Hayato screams that it's all his fault that they got involved in this mess. He'll take care of Claw, they need to escape now! Ryo and Katsumi flee down the ruined hospital's corridors. Suddenly Ryo stops. He tells Katsumi to run home, he's going back to help Hayato. Katsumi protests that's too dangero

As the twins continue their rampage throughout the school, Hayato is stuck fighting Plus, while Minus comes out of the ceiling and engages Ryo. Plus and Minus overwhlem their opponents, but Takeshi appears and turns the tables around.

Keith, the mysterious Egrigori agent, makes his prescence felt after knocking out Hayato. Al sends Minus after him, but Keith easily defeats Minus, and kills Jeff. But when he turns to Al, Takeshi saves him with White Rabbit speed. Keith leaves, but leaves an invitation to the ARMS users to go to Abumisawa village, site of the deaths of Hayato's parents. To get more advice, they go to Juzu Shingu, master of the Shingu fighting style, for information on ARMs, Egrigori, and Abumisawa. Al joins the team, on the condition that they cooperate in his experiments to find out what ARMS are made of. After Juzu takes out Takeshi and Hayato, Ryo nearly catches Juzu with Jabberwock. After a few parting words with Juzu, the gang goes to Abumisawa, with Katsumi sneaking off with them. Their trip gets more exciting when they are held hostage by armed militia bent on preventing them from going to Abumisawa.