Cain (a.k.a CN-7 Model Combat Robot) met the Rust Crew in a cop chase in the Upper City of Tokyo, accompanied by his partner Jean. The chase is interrupted by a road block, making the car crash, killing Jean and placing the Rust Crew amidst an ambush. Cain becomes a party member shortly after Jean's death. He is the most resistant party member and is recommended to situations like ambushs.
After the ambush, the Rust Crew goes to the rooftop of a buliding, where Cain uses a wire gun to go to another building. However, Detective Kurosawa shoots the wire when Dan and Faye are using. Dan is able to land into the top of a train, and Cain saves Faye. His relationship with Dan is not very good at the beginning, and even though the rest of the crew acknowledge Cain is an extremely helpful party member, Dan seems reluctant to admit that, calling Cain "scrap-head" and "showoff".
However, at the Amada building, when Cain is controlled by Amada (Cain is built by the Bergen Industries, and since Bergen stole his codes from Amada, the Bergen robots can be controlled by Amada.), Dan is worried about Cain's fate. If your trust with Cain is high enough (three full trust bars - along with the rest of your squad members), he will survive and help Dan in the final battle, but if your trust with Cain is low, Cain is not seen again in the story.
Cain's interest in emotions and human relationships are quite big, and he demonstrate these interests when he sees Dan kissing Faye, and states that Jean treated him very badly, maybe because Jean didn't have a lover. However, he states that he can't comprehend emotions, and when exposed to suffering in the Amada Building, Cain breaks down and succumbs to Amada.