Shun Watanabe, also known as Hayabusa Watanabe, becomes president of Musashino Animation following Masato Marukawa's resignation. He assumes leadership after the studio's original anime series *Time Hippopotamus* is canceled due to sponsor financial issues. As president, Watanabe steers the studio through a challenging transition, initiating production of the original feature-length anime film *Air Amphibious Assault Ship SIVA* for a February 2020 release. Recognizing her capabilities despite the demanding nine-month schedule, he specifically assigns Aoi Miyamori to lead the project as producer. Watanabe collaborates closely with Western Entertainment producer Gōtarō Katsuragi on the film's budget and production challenges, especially after the initial studio GPU fails to deliver storyboards.

When GPU President Yoshio Misaki later asserts joint rights to the film, threatening production, Watanabe participates in strategic discussions with Miyamori, Kaede Miyai, and Katsuragi to resolve the contractual dispute. He supports Miyamori and Miyai as they confront Misaki about contract violations, ensuring the film continues primarily under Musashino Animation's leadership. Watanabe's leadership provides stability during the studio's crisis, extending beyond administrative duties. He endorses Miyamori's decision to remake the film's ending despite the looming deadline, prioritizing artistic satisfaction. His surname, Watanabe, combines the characters for "cross, ferry" (渡) and "edge, side" (辺), reflecting themes of navigating challenges.