Masashi Irinatsu, a third-year Musical Department student at Ayanagi Gakuen High School, serves on the Kao Council. He sports blond hair, blue eyes, and dark skin, frequently donning black headphones and a black shirt beneath his council coat. As the most vocal new council member, he actively observes second-year students and initiates efforts to ease internal tensions. His personality radiates loyalty, sympathy, and camaraderie, making him the first council member to genuinely appreciate Hoshitani and his peers. He often mediates conflicts with a warm, approachable demeanor.

Irinatsu's family holds significant influence in the music industry; his parents are prominent figures who own a professional studio, later utilized for training Team Hiragi during breaks. Inheriting their musical aptitude, he excels in composition and confidently crafts songs like "SILENT FEVER" for Opening Ceremony teams.

During his first year, he belonged to a General Team, sharing this background with Shion Kasugano. His habits include snacking during meetings—irritating Ryo Fuyusawa—and reacting intensely when angered despite a forgiving nature. He relieves stress by playing piano vigorously in soundproof rooms and enjoys running for travel. His favorite foods are shaved ice and Okinawan chanpuru, a stir-fry his grandmother prepared.

Notably, Irinatsu sought dismissal from the council following Toma Shiki’s removal but reversed this decision after Shiki’s reinstatement, underscoring his principled loyalty. Academically, he excels in music, Japanese, and English, crediting lyric-writing as a factor. He claims no subject weaknesses, stating he "loves everything."