Makoto Ninomiya is a main character from Amanchu! and a student at Yumegaoka High School. He is the younger twin brother of Ai Ninomiya, and the siblings are one year older than the protagonists Hikari Kohinata and Futaba Ooki. Makoto is a member of the school's scuba diving club, where he serves as a senior member alongside his sister. In terms of background, he is introduced as a calm and composed individual who often hangs around with Ai, though his quiet demeanor is not due to shyness but rather a cautious awareness of his sister's quick temper. His personality is defined by being gentle, unfailingly kind, and a steady voice of reason among the more excitable characters in the series. He frequently finds himself on the receiving end of Ai's stress-fueled outbursts, yet he never wavers in his protective care for her. Makoto's primary motivation revolves around his love for diving and the ocean; he embarks on underwater adventures that help him discover a deeper sense of self and connection to the world. His role in the story is that of a supportive figure and a reliable senior to Hikari and Futaba, often welcoming them with benevolence and helping guide their experiences in the diving club. His key relationships include his twin sister Ai, whose fiery personality contrasts sharply with his own calmness, and the younger divers Hikari and Futaba, whom he treats kindly as his juniors. Over the course of the series, Makoto shows subtle development, becoming more expressive of his emotions while maintaining his composed nature, and his passion for diving continues to grow. Notable abilities include his proficiency in scuba diving, his deep knowledge of marine life, and his ability to remain level-headed and dependable even in challenging underwater situations.