Ichiban Natsuno attends Meisei Academy alongside Otomi Tachibana. His name, meaning "Number One Summer," reflects his singular ambition: pitching in the Summer Koshien tournament. As the Ace pitcher for Meisei's baseball team following Toma Tachibana's graduation, he commands the mound with intense dedication. This deep-seated passion for baseball leads him to regularly neglect his studies, causing academic difficulties and drawing teacher criticism, especially when team commitments cause school absences.

Natsuno nurses a fervent crush on Otomi, who remains oblivious to his feelings. His attempts to express affection or shield her, such as intervening with rivals like Ryo Akai, consistently escape her notice. Demonstrating this protective instinct, he once faked illness to skip class solely to attend a crucial team game, highlighting his prioritization of baseball above all else. Natsuno exhibits a determined and enthusiastic personality, channeled into relentless effort on the field and unflinching focus on reaching Koshien.