Masayuki Koshino is a third-year student at Fujimori Academy and serves as the vice-president of the student council. He is notably strong, a trait that is both physical and indicative of his dependable nature. Koshino is characterized as a balanced, reliable, and sincere individual who takes his responsibilities seriously. Because of these qualities, he earns the respect of his peers. He is deeply loyal and dedicated to his duties, often placing the needs of the council and the school above his own preferences. Koshino shares a particularly close bond with Tohru Kouno, one of the school's Princesses; he regards Tohru almost as a younger brother, while Tohru looks up to him as a protector and role model. Koshino also works closely under student council president Shuya Arisada, supporting his initiatives. Over the course of the story, Koshino fulfills his role as vice-president until his graduation, which takes place in the sequel series Princess Princess Plus. His physical strength and steadfast sense of duty make him a reliable pillar of the student council.