Kojirô Shinomiya is a graduate of the Totsuki Culinary Institute, where he held the First Seat in the elite Council of Ten Masters as part of the 79th generation. After graduating at the top of his class, he moved to France and, following six years of intense training, opened his own French restaurant in Paris named SHINO'S. He became the first Japanese chef to be awarded the Pluspol Medal, a prestigious honor recognizing significant contributions to the advancement of French cuisine, and he later achieved the distinction of earning three Michelin stars for his restaurant. His initial motivation to pursue French cooking was rooted in a childhood memory of wanting to recreate the happiness his mother showed when she ate a French meal.

The discrimination Shinomiya faced in France as a Japanese chef caused him to develop a harsh and extremely rigid personality. He became known for his narcissistic pride, a demanding and perfectionistic nature, and a strong superiority complex. He is deeply sensitive to any criticism of his cooking philosophy and insists on traditional French methods, believing that using the original, authentic ingredients is the only way to achieve the true essence of a dish. Despite this formidable exterior, he possesses a deep-seated need for recognition and cares deeply for the few individuals who earn his respect.

Within the main narrative, Shinomiya first appears as a guest instructor during the Totsuki Friendship and Rapport Training Camp, where he functions as a powerful antagonist and a benchmark for professional excellence that the protagonist Soma Yukihira must strive to reach. Their initial antagonism evolves into a master-apprentice relationship during the Stagiaire arc, when Soma trains in the kitchen of SHINO'S. Shinomiya also shares a pivotal connection with Megumi Tadokoro; her cooking, filled with warmth and consideration, serves as a catalyst that forces him to recognize his own creative and emotional stagnation. He maintains a teasing, combative friendship with his junior Hinako Inui and a mutual, competitive respect with his peer Fuyumi Mizuhara. He holds his senior Gin Dojima in high regard as a guiding figure.

Shinomiya undergoes significant development as he overcomes a period of stagnation. The confrontations with Soma and the insight gained from Megumi's cooking push him to abandon his isolated, prideful stance and reconnect with the emotional power of food. This reinvention allows him to achieve three Michelin stars and transforms him from a solitary genius into a supportive mentor who nurtures the next generation of chefs. He is widely known as the Légumes Magician, or the Vegetable Magician, for his extraordinary ability to make vegetables the star of his haute cuisine. His abilities are rooted in an encyclopedic knowledge of vegetable varieties, seasons, and the precise classical French techniques needed to draw out their maximum flavor and visual beauty.