Many doujinshi covers feature gratuitous fanservice to attract buyers.
Doujinshi (also spelled dōjinshi) are self-published Japanese works, such as manga, novels, and artwork.
Doujinshi are often based on characters and settings from existing professional/commercial works. In the case of artwork, these are called fan art, in the case of stories, fan fiction.
Doujinshi is also a Japanese manga magazine published by fans, as such tend to be noncommercial.