Perhaps most notably, by offering works that arguably “push the envelope” more than the works of the formal manga industry, dōjinshi may produce examples of innovation that create new opportunities for the entire industry. Indeed, mainstream manga publishing companies have in the past brought the styles and ideas of “hot” subcultures into their own product lines. New genres fostered by the dōjinshi markets– genres that are often quite risqué – have been at times been adopted by mainstream commercial manga publishers.
Mehra, Salil. 2002. “Copyright and Comics in Japan: Does Law Explain Why All the Cartoons My Kid Watches Are Japanese Imports?” SSRN eLibrary.
Mehra’s paper is fifteen years old, but it’s still a great explanation of the legal position of fanworks in Japan, and why these fanworks show that letting fans create (and even sell) work freely makes economic sense for media companies. One of those reasons is that fanworks are a hotbed of content innovation that companies can take advantage of. The most famous example of a dōjinshi genre that was adopted by the mainstream manga industry is probably yaoi, the Japanese equivalent of slash, which inspired the massively popular commercial manga genre called BL/boys’ love.
I highly recommend this paper for anyone looking to learn more about Japanese law and fanworks.