Doujinshi are often published in manga format and are a comic that is not commercially published.
Doujinshi have been around since the late 1800s and they have their origins in Japan, but their popularity has spread to other countries as well. They are typically self-published by amateurs. They usually feature characters from an established manga series or from a well-known Japanese anime or video game.
Doujinshi can be a great way to introduce people to new artists and shows. It provides an excellent form of promotion for people who want to share their original creations with others as well as engaging with other people.