Tetsumasa Amino, commonly called Tetsu, serves as both classmate and one of Karada Iokawa's closest friends. He possesses auburn or maroon hair extending to his neck and green or gray eyes, coupled with a notably tall stature for his age that occasionally prompts others to mistake him for a high school student. His typical attire includes casual tank tops, pants, and sneakers. Tetsu harbors romantic feelings for Karada but struggles to voice them openly. When Karada mysteriously vanishes after her transformation into an adult, he neglects his studies and frantically scours their town to locate her, displaying evident concern for her well-being. He exhibits visible frustration toward her older brother Hiro during Hiro's interference in their interactions. Tetsu has an older sister, Tōko Amino, who works at a local café frequented by Hiro. The manga adaptation significantly expands his role compared to the anime, portraying his relationship with Karada as more complex and problematic.