Jō Kitahara is a central character in the Uma Musume: Cinderella Gray storyline, serving as the determined and often conflicted trainer for the talented horse girl Oguri Cap. His story begins at the Kasamatsu Tracen Academy, a regional racing circuit where he has long harbored a singular dream of winning the Tokai Derby, the most prestigious local race. For years, this goal seemed out of reach, with the academy lacking a horse girl of sufficient potential to inspire him, leaving him feeling disillusioned with the stagnant regional scene. This all changes when he witnesses the raw, untapped ability of the new student, Oguri Cap, during a practice run. Deeply moved and excited for the first time in ages, he immediately scouts her, also taking on her quiet friend Belno Light as a member of his small team.

Personality-wise, Kitahara is presented as an earnest and passionate individual, though his journey is marked by a profound inner conflict between personal ambition and the responsibility he holds for his pupil. He has a sharp eye for talent and a good deal of technical insight as a trainer, creating effective regimens that allow Oguri to win races by significant margins early in her career. However, his experience is limited to the regional level. This inexperience and his intense focus on his own dream lead to a pivotal moment of weakness. When Oguri's dominant performances attract the attention of the central circuit's elite, represented by Symboli Rudolf, Kitahara is confronted with a painful reality: Oguri has outgrown him. He lacks the necessary license to train at the national level, meaning that for her to reach her true potential, she must leave him behind.

Unable to reconcile this, Kitahara makes a desperate and ethically questionable decision. He gives Oguri an ultimatum, telling her that if she wins her next race, she must transfer to the central circuit, but if she loses, she will stay with him in the regions. This moment highlights his most human flaw, his fear of losing his dream and his identity as her trainer. The weight of this burden visibly affects Oguri's performance during the race. Watching her struggle, Kitahara has a change of heart. He realizes the unfairness of his demand and, in a cathartic outburst, cheers her on to run with everything she has, urging her to chase her own destiny on the national stage. This act of selflessness marks a turning point in his character development. His shattered dream of winning the Tokai Derby is replaced by a new, more selfless goal: to become a trainer worthy of Oguri Cap.

From this point, Kitahara's role shifts from being the primary trainer to a supportive figure working to reunite with his charge. He remains behind at Kasamatsu, dedicating himself to studying for the difficult national trainer's license exam, while his experienced uncle, Ginjirō Musaka, takes over Oguri's training at the prestigious Tracen Academy in Tokyo. Despite the distance, Kitahara's bond with Oguri remains a powerful emotional anchor for her. He continues to support her from afar, visiting her when she faces slumps and offering honest encouragement, even confessing to her when he fails his first licensing exam. His dedication is eventually rewarded when he passes the exam and finally earns a position as a sub-trainer on his uncle's team, allowing him to once again be directly involved in Oguri's career as she faces the toughest challenges of her racing life. Beyond his relationship with Oguri, his dynamic with his uncle, Musaka, is key, with Musaka acting as a gruff but wise mentor who pushes Kitahara to be better and to make the right choices for the horse girls in his care. In the end, Jō Kitahara is defined by his journey from a man chasing a personal dream to a genuine mentor who learns that a trainer's greatest success lies in the growth and happiness of the athletes he supports.