Short answers, pulled from the story.
Mitsuyo Seo was born in 1911 and worked as a sign painter before entering animation. He painted advertisements for local businesses in Tokyo, which required a steady hand and an eye for detail.
Mitsuyo Seo was arrested in 1931 for his activities with the Proletarian Film League of Japan. He spent 21 days in jail after being tortured for his commitment to highlighting the struggles of the working class.
Mitsuyo Seo released Ari-chan in 1941, which was the first Japanese work to fully utilize the multiplane camera. This technology allowed animators to create depth and three-dimensional space by moving different layers of animation at different speeds.
Mitsuyo Seo created Momotarō: Umi no Shinpei, which is recognized as Japan's first real feature-length animated film. The film has a runtime of 74 minutes, making it longer than the 37-minute Momotarō no Umiwashi.
The film Ousama no Shippo was released in 1949 but was left without a distributor by Tōhō. The bankruptcy of Nihon Manga Eigasha followed shortly after, leaving Seo without a platform to continue his work in animation.