The current first Seat of the Elite Ten. Erina's former arch-nemesis who hails from the humble Yukihira Diner, Sōma is Erina's main rival. Erina was the Elite Ten member who supervised the Entrance Exam that Sōma applied in. Erina quickly deemed Sōma a second-grade cook due to his diner background, and was initially insulted by the outward simplicity of his dish. While Erina was impressed by Sōma's dish, but a mixture of her pride and Sōma's cocky attitude led her to deny him entrance to the school. To her shock and fury, her decision was overridden by Senzaemon, and Sōma joined her as part of the 92nd class. Erina went out of her way to make Sōma's life at Tōtsuki as difficult as possible, or at least try to remind him of their difference of status. Unfortunately for her, her attempts at intimidation were ineffective against the happy-go-lucky Soma who either ignored her insults or, due to his denseness, misunderstood what she's trying to say, further infuriating Erina. Any mention of Sōma's name or merely being in his presence would send Erina into a state of frustration and anger to the point that Hisako would avoid referring to him as much as possible.
Despite Erina's hostile behavior to Sōma, Sōma himself showed no hostility towards her, having a one-sided friendly attitude to her. At times though, Erina does acknowledge that Sōma is skilled, though she still views him lower than her due to her pride. Erina was unaware that Sōma is also the son of her idol, Jōichirō Saiba, though she did once see a visage of Jōichirō over Sōma. His relationship to Jōichirō is inadvertently revealed to her when she walked in on a conversation between her father and Sōma. At first, she was in disbelief but realized it was true after seeing the two next to each other in a recent photo. She became greatly shocked after realizing that she had been hostile towards the son of the chef she always admired.
After Sōma gave her a taste of true Yukihira cooking, Erina has become much more friendly to Sōma, enough so to give him personal lessons in order to prepare himself and the other 92nd Generation standouts in order to pass the Promotion Exams. She tends to talk more personal things with Soma when they're alone and she no longer gets angry when she sees him or when someone mentions his name. She even laughed at some of his antics.
During her match with Momo, Erina seemed to have used Sōma as inspiration to make a dish through innovation and even used his victory catchphrase after winning her match. Sōma noticed this and teased her about it, only for Erina to react defensively. While the two can function as a team, they also tend to clash and butt-heads whenever one or the other will battle their opponents. While she will not admit to it, Erina realized that she wanted to become a chef like Sōma proven on how her usual behavior quickly changed as she remade her entree dish, was that of Sōma's look of having fun. During the final bout, Erina even used Sōma's "Transforming Seasoning" for her final dish, which greatly satisfied the judges by giving them the same reaction she received from Sōma's entry dish, as well as naming her dishes on the spot and with Erina asking her father how does her new dish taste.
Following the Rebels victory, Erina angrily chastises Sōma for forcing her to make up a specialty dish in order to win, but is thankful in his faith in her as well as his efforts and contributions to help her win. Upon appointing a 1st Seat candidate, Erina chose Sōma as she believed it was his efforts, faith and innovation that led the Rebels to victory. He then nominates Erina as the new Headmistress of Tōtsuki as Sōma claims that she is still stronger than him, but also to give him a reason to challenge her in the future.
During their 2nd year, the two share a good camaraderie friendship with Sōma acting as Erina's right hand man. After Asahi's princely demeanor as well as Sōma declaring claim of Erina, she began feeling confused and flustered over the two young men fighting over her. While she may not have realized it, Erina seems to have Sōma constantly in her mind as when she was describing her ideal man to Megumi, she was actually describing Sōma. The two began speaking after Sōma became concerned about her leaving him, prompting the two to have their usual talk. While he compliments her smile, referring to her happy self as pretty, Erina became shocked and flustered while trying to maintain her focus on the task at hand. Sōma and Erina reaffirm that they will continue their journey together, hoping to stay by each other's side.
In the epilogue, Erina gets a call from Sōma telling her that he's returning to Japan and plans to challenge her again, to which she gladly accepts by calling all of their friends to oversee them. According to Sōma's grandfather, Erina has always been accommodating for him whenever he gets a new idea, though she tries to justify that as dean/headmistress of the academy she is obligated to help all students, alumni included. As she waits for Sōma at the diner, Erina begins to contemplate her reasoning for always helping Sōma, as she remembers during their 3rd year she was infuriated that he left her a note as he suddenly went abroad. Admitting to herself that she believed he would stay with her competing and cooking together, but felt sad and disappointed that he left without saying a word to her. However, Erina seems genuinely happy to see him again and even admits that she genuinely became more interested to see Sōma again and taste his dishes every time they meet. She then asks for his specialty dish as she desires his best cooking as the chef she has admired for years.
Tsukada, the creator of Food Wars, confirmed that Soma and Erina were canon and are eventually married in an interview, despite not having showed they were canon in the final chapters of the manga.
SouEri is an exceptionally popular ship among the Food Wars community, with many fans, both for and against, agreeing that SouEri was a near certain outcome. This ultimately led to surprise among the community that the manga did not end with them as a couple.
The rival ship to SouEri is SouMegu. Although by no means a rival, SouEri shippers hold great hatred for Asahi, who attempted to court Erina and marry her, and for effectively interfering in Soma and Erina's relationship.
On AO3, SouEri is the most written ship for Erina and the second most written for Soma. It is also the second most written ship in the Food Wars tag.
- The decision by the author of Food Wars, Yuto Tsukuda, not to officially pair Soma and Erina together within the manga was met with widespread criticism across the fanbase and a great sense of disappointment, as many believed the series was building towards that outcome.
- The author stated, in the final epilogue of Le Dessert, that he wished for Soma and Erina to get married but felt he could not fit it into the storyboard at the time.
- When Joichiro Yukihira said, "Listen well, Soma, the secret to becoming a great chef is... meeting a woman that will make you want to give all the food you make to her..", the next shot is of Erina.
- During the fifth ending, Atria, the main cast can be seen running alongside the train with Erina in the lead. Eventually, Soma catches up to her and starts running beside her, with Megumi and Aldini in tow, she then looks at Soma and notices his smile and decides to smile herself. This is almost certainly a reference to Soma helping her find the joy in cooking.
- In the alternate cover art for Volume 36, Soma is seen feeding Erina one of his dishes.