Sōma is Jōichirō's son. In his son's youth, he was amused by his desire to become a great chef like him. Although Jōichirō thought that Sōma would grow out of that phase, he was amazed by his son's tenacity to continue cooking despite numerous cooking duel losses. Jōichirō gave Sōma a little bit of training, but for the most part, left Sōma to develop his cooking skills on his own. For most of Sōma's life, surpassing Jōichirō was Sōma's ultimate goal. Upon reaching the high school level, Jōichirō closed Restaurant Yukihira to force his son to attend Tōtsuki Culinary Academy, knowing that it was the best way for Sōma to achieve his goal.
Though Sōma has yet to defeat his father in a cooking duel, Jōichirō remains supportive in his son's goal. At the same time, Jōichirō has admired Sōma's tenacity, stating that even he lacked the same drive, passion, and courage to face trials head-on. Jōichirō has always expressed confidence in Sōma's abilities and potential but still takes time to heckle him to keep him humble.
Not much is known about the relationship between Jōichirō and his wife or even how they met. What is known, however, is that she was instrumental in Jōichirō's psychological recovery from his near mental breakdown at Tōtsuki to the point that he took up her surname instead of the other way around. According to Fumio Daimidō, his cooking has a softer feel to it than in his school days, suggesting that she was responsible for that as well. She is also the inspiration towards Jōichirō's advice to Sōma of cooking for someone to elevate his ability.
Gin is Jōichirō's best friend since the two attended Tōtsuki over 20 years prior to the start of the story as a part of the 69th generation. The two were central pillars of the Polar Star Dormitory's golden era and Gin and Jōichirō eventually acquired the 1st and 2nd seat of the Elite Ten Council respectively by their third year.
Despite their close bond, Jōichirō barely kept in contact with his old friend, much to Gin's frustrations. Nevertheless, the two warmly greeted each other during their first meeting in years, indicating that they are both quite close.
Back in their school days, Dōjima was irritated with Jōichirō's childish antics and irresponsibility. Many years later, when Jōichirō and Gin train the rebels, those feelings resurge.
During his time at Tōtsuki, Jōichirō had the unfortunate habit of creating unusual and often horrifically disgusting dishes. Though Jōichirō used whoever would volunteer, Jun in particular was his most prolific taste tester during his time at Tōtsuki. Though Jōichirō remembered those times fondly, Jun developed deep emotional trauma as a result of her extensive, and sometimes forced, taste testing. The trauma was so severe, she lashed out and punched Sōma the minute she found out that he was Jōichirō's son. While she later got used to Sōma, her dislike of Jōichirō remains.
Azami is Jōichirō's kouhai who was the 3rd Seat of the Elite Ten Council when Jōichirō was a third year 2nd Seat. It is not known exactly how Jōichirō feels about Azami other than him expressing shock that he replaced Senzaemon as Headmaster of Tōtsuki. However, inversely, Azami holds a deep respect for Jōichirō. In a similar fashion to his daughter, Azami believes that Jōichirō was a one-of-a-kind chef, nothing less than the image of a perfect chef in his mind. In fact, his motives towards Tōtsuki are in his mind in the name of vengeance on the current culinary world as he believe that it was the cause of Jōichirō leaving Tōtsuki in the first place.
Jōichirō doesn't seem to approve of Azami's ideals as he had no qualms in training and whole-heartedly supporting the Rebels against Azami's Central.
Over 20 years prior to the start of the story, Fumio was still the dorm mother when Jōichirō was attending Tōtsuki. Fumio cared a great deal for Jōichirō as he was one of the best residents in the history of Polar Star, even being considered a central pillar of the Golden Era.
After his departure from Tōtsuki, Jōichirō remained somewhat in contact with her, usually wandering into the dormitory whenever he pleased. However, it is apparent that their contact wasn't too long as she was unaware he fathered a son until a recent visit from him.
Fumio often likens him to a stray cat because he comes and goes at will as opposed to Gin who is like a loyal dog and is annoyed his habit of making bad dishes remain and he passed it down to his son. Nevertheless, Fumio still thinks of Jōichirō fondly, signifying a strong bond between the two.
Jōichirō met Isshiki during his stay in the Polar Star Dormitory after his trip abroad, the 7th seat was impressed that he got to talk and eat Jōichirō's dishes because of the latter's fame and stories as a nomad or wandering chef who cooked around the world.
His relationship with Jōichirō is that of a senpai-kouhai, they both seem to find Sōma as a topic for their talks and discussions.
After establishing Restaurant Yukihira, Jōichirō spent some time as a freelance chef and eventually worked for the Nakiri Mansion. During his time there, he met a 10-year-old Erina. Though his time there was short, his cool personality and unorthodox cooking enthralled Erina, becoming her cooking idol. Before leaving the mansion, the two took a photo which has been Erina's greatest treasure. Additionally, Jōichirō made a promise to Erina to eat her dishes once she had become a great chef herself. It is not known if Jōichirō remembers this promise, but for Erina, this has been one of her greatest motivations to become a chef.
As a former member of the Elite Ten Council, Jōichirō became acquainted with Senzaemon. Despite the fact that he never graduated from Tōtsuki, Senzaemon showed clear confidence in his skills, hiring him as a temporary chef from the Nakiri Family when his granddaughter was around 10 years old. Around the time of 92nd Tōtsuki Generation's entry into the high school section, Jōichirō had remained in contact with Senzaemon as it was because of his suggestion to Jōichirō that Sōma would eventually attend Tōtsuki. It was also Senzaemon's suggestion that Jōichirō leave Tōtsuki and Japan to travel the world after Senzaemon saw how burnt out Jōichirō had become in the middle of his third year of high school.
Jōichirō and Asahi met each other 10 years ago in America. Jōichirō would somehow treat Asahi like his own child and both of them would meet up every time Jōichirō visits America. Additionally, Asahi is the only chef that Jōichirō has considered as his disciple.