Faith was assigned to prosecutor Jacques Portsman as his investigative partner. Portsman proceeded to refer to Faith as "Jim", a name he used for all detectives assigned to him. Portsman felt that "Jacques and Jim" sounded better than "Jacques and Buddy". The two would often play sports, such as basketball, with each other. However, Faith was never able to make a shot since he was only allowed to pass to his superior. When told about this, Miles Edgeworth thought that Portsman viewed the detective as more of a pet than a partner.
When Ernest Amano was about to be arrested by Shi-Long Lang, Portsman and Faith appeared to take him away. This was because, in actuality, both Portsman and Amano were part of an international smuggling ring, and thus Portsman was tasked to protect Amano from the law. In order to perform this task, Portsman had Faith obtain three pieces of evidence for him: a gun, a pendant, and a video tape. Both the gun and the pendant were important pieces of evidence in the case against Amano. The video tape, labeled "KG-8 Incident" and stained with Faith's blood at the time of his death, would later aid in the arrest of Quercus Alba, the leader of the smuggling ring.
Faith returned to Portsman's office with the three pieces of evidence, but finding that his superior was out, he left a note that he had gotten the three items and would meet up with him later. The detective then heard the sound of someone moving about in Edgeworth's office, which he found suspicious since the prosecutor had not yet returned to his office. He entered Edgeworth's office to find Portsman ransacking the room. Faith confronted his superior and, in the struggle, Portsman took the detective's police-issued pistol from him.
Portsman asserted that a prosecutor's job was to find the accused guilty. Faith asked why Portsman was doing what he was doing, only to be told that the prosecuting prodigy would use any means necessary to obtain a guilty verdict, before promptly being shot. The bullet passed through Faith's lower abdomen and into the bookcase behind him. "Jim" fell back against the bookcase and collapsed, dead. Portsman then wrote "Gumshoe" in Faith's blood on the books beside Faith's body in order to point the finger of blame at detective Dick Gumshoe.
Edgeworth was shocked to find Faith's body in his office and proceeded to investigate the case. Despite Portsman accusing Edgeworth, Gumshoe, and Maggey Byrde of the murder, Edgeworth was able to expose Portsman as the true killer.
Faith appears to have been submissive when it came to following Portsman's orders. However, the confrontation with Portsman that resulted in Faith's demise indicates that he was a good man, shocked at the behavior of his superior. Concerning the tape, Faith's actions in Edgeworth's office appear to show that he was just blindly following orders.
His Japanese name may come from the phrase "nakama to shinjiteiru" meaning "I trust him as a friend" or "I believe he is a friend".
His English name "Buddy" is indicative of the seemingly friendly relationship between Jacques Portsman and Buddy Faith. The fact that "Buddy" is also a common dog's name may be a hint to the Faith's submissiveness to Portsman.
"Faith" indicates his (misplaced) devotion and confidence in his investigative partner.
"Jacques and Jim" could be a reference to the nursery rhyme Jack and Jill.
Faith's nickname "Jim" may also be a pun on the word "gym", following a similar theme to Jacques Portsman's name being a play on "jock sportsman".