Amateur creations are one source of Japan’s competitiveness in the content industry. This study summarizes prior research on amateur manga (comic), called doujinshi, in terms of its history and current status, overseas trends, gender aspects, and copyrights. This study then develops a research model with three hypotheses on the relationship between creation and monetization across multiple content categories. To test these hypotheses, an online survey of 2,593 individuals was conducted on the creation and monetization of manga and music. The survey’s findings were as follows: (1) Consumers who create works in one content category tend to do so in other categories. (2) Consumers who monetize their own work in one content category tend to do so in other categories. (3) Consumers who create works in multiple content categories tend to monetize their own works. This study also shows the current status of creation and monetization in Japanese manga and music.