Porco Rosso, a Studio Ghibli film made in 1992, originally planned as a short in-flight film for Japan Airlines based on Hayao Miyazaki's manga The Age of the Flying Boat, but grew into a feature-length film.

It is based on "The Age of the Flying Boat", a 15 page, three-part 1989 watercolor manga by Miyazaki that also inspired Disney's Duck Tales

https://en.wikipedia.org/wiki/Porco_Rosso

https://en.wikipedia.org/wiki/Hik%C5%8Dtei_Jidai

https://www.pdf-archive.com/2016/07/23/hikotei-jidai-the-age-of-the-flying-boat/hikotei-jidai-the-age-of-the-flying-boat.pdf

https://podcasts.apple.com/us/podcast/porco-rosso/id1381507437?i=1000562427727

https://www.rotoscopers.com/2017/04/03/studio-ghibli-countdown-porco-rosso/