Isami Aldini is the fraternal younger twin brother of Takumi Aldini, born into a Japanese-Italian family in Italy. Both brothers grew up working at their family's Trattoria Aldini, where Isami developed an early inferiority complex despite excelling outside the kitchen. While Takumi frequently received customer requests for his dishes, Isami struggled to match his brother's culinary skill. This dynamic culminated in an incident where Isami altered one of Takumi's dishes, unintentionally dulling its flavor and earning a reprimand from their father. Takumi consoled him, emphasizing their essential partnership for the restaurant's success, leading them to vow making Trattoria Aldini Italy's top restaurant together. Physically, Isami undergoes noticeable seasonal changes, becoming heavier during autumn and winter while slimming down significantly in spring and summer due to heat and activity. After an intense summer of practice in Japan, his weight loss became permanent, accompanied by a growth spurt that increased his resemblance to his twin. His brownish-black hair is spiky and combed backward. His facial features shift between a lighter, sharper appearance when slim and a rounder look featuring distinctive shark-like teeth when heavier. In personality, Isami contrasts Takumi's fiery competitiveness with a calm, jovial, and supportive demeanor. He maintains a peaceful disposition and easily befriends others, including rivals like Sōma Yukihira and residents of Polar Star Dormitory. Despite his generally cheerful outlook, he harbors deep-seated insecurity about his culinary abilities compared to Takumi. This insecurity fuels his determination to improve, particularly after witnessing Takumi's defeats. He often teases Takumi about impulsive actions yet remains fiercely loyal, serving as his brother's sous-chef and emotional anchor during high-pressure situations. At Tōtsuki Culinary Academy, where both brothers enrolled on their uncle's recommendation, Isami partnered with Takumi during the Friendship and Rapport Training Camp. They created dishes like "Aigamo Grilled with Spices," demonstrating seamless teamwork and skill with the mezzaluna knife. Isami's calmness balanced Takumi's intensity, notably during challenges like the breakfast buffet assignment where he urged Takumi to rest before the final task. For the 43rd Tōtsuki Autumn Election, Isami stayed in Japan over summer break for independent training, losing weight permanently under intense heat and pressure. During the preliminary round, he crafted an innovative "Curry Bread Calzone," combining Japanese curry with Italian calzone dough. The dish impressed judges with its fusion approach and momentarily outshone Takumi's entry, though Takumi ultimately scored higher. This period marked a turning point for Isami's confidence and independent growth. Later, during the Moon Banquet Festival, Isami collaborated with Sōma Yukihira by preparing noodles for one of his dishes, showcasing adaptability and willingness to support allies beyond his partnership with Takumi. His role expanded during the regiment de cuisine against Central, contributing to the rebel efforts alongside his brother. By his third year, his development culminated in earning a seat on the Elite Ten Council, reflecting his growth into a respected chef.