When Seo (1911-2010) decided to become an animator he was turned away by the largely family-run companies. He joined Prokino, the leftist proletarian film group that was brutally suppressed in the early 1930s, with Seo suffering at least one arrest. He later worked with Masaoka Kenzo until he started his own company in 1935, where he made Norakuro and other cartoons until his firm was absorbed by Geijutsu Eigasha. After making what was billed as Japan’s first feature-length animation, Momotaro’s Sea Eagles (1942), he joined Masaoka at Shochiku to make Momotaro’s Divine Sea Warriors (1945), which was released only four months before the end of the war, but influenced many artists, including the manga master Osamu Tezuka. Seo attempted to continue in animation after the war, but with Japanese animation depending a lot on wartime government support, peace drove him and many others like Masaoka out of the business.