Atsuhiko Yamada is a third-year high school student and a talented competitive diver who belongs to the Miyagi Spirits club, which is a rival team to the Mizuki Diving Club (MDC). He is widely known by the nickname Pinky, a reference to his distinctive and bright pink swimsuit. Physically, he is characterized as an adolescent male with brown hair that is cut to ear-length and black eyes.

Yamada is defined by his intense and ultimately one-sided rivalry with Youichi Fujitani, a prodigious diver from the MDC. This fixation began after their first competition together, in which Fujitani became the first person to defeat him. Since that loss, Yamada has been singularly obsessed with the goal of beating Fujitani at least once, frequently challenging him in various contexts both in and out of the water. His personality is theatrical and relentlessly over-the-top, often shouting dramatic declarations, such as vowing to send his opponent to hell with his diving.

Despite his immense skill, Yamada has a critical psychological weakness. He is known to be an excellent diver who, according to his rival Fujitani, could be the best in Japan if not for his tendency to become completely paralyzed by stress during competitions. This pressure is self-inflicted, as he becomes so hyper-focused on his rivalry that he cannot perform to his full potential under the weight of his own expectations. His background in dance has granted him exceptional flexibility and freedom of movement, which contributes to his technical prowess in the sport. He is also noted for performing tricky dives. His role in the story is primarily that of a rival and a source of character-based comedy, acting as an elite guest athlete who comes to train at the MDC and stir up competition.