In 1971, animators Hayao Miyazaki and Isao Takahata began preproduction on an adaptation of Astrid Lindgren's Pippi Longstocking books, but in the end, were unable to secure Lindgren's permission. But we can still see Miyazaki's watercolor concept art of the strongest girl in the world.
The Miyazaki and Studio GHIBLI LiveJournal has more concept images from the never-made film Pippi Longstocking, The Strongest Girl in the World. The illustrations are a rather marvelous combination of Lindgren's character and Miyazaki's style, but after Lindgren met with Miyazaki and Takahata, she declined to give them permission for the adaptation. Of course, we're not seeing the entire pitch here, so we don't get a full sense of what the animators planned to do with Lindgren's work.
But Pippi's influence would be felt in later Miyazaki and Takahata ventures, notably in Panda! Go, Panda!'s Mimiko, with her pair of red braids.