Doujin music

Doujin music (同人音楽, dōjin ongaku), also called otokei doujin (音系同人) in Japan, is a sub-category of doujin activity. Doujin are non-official self-published Japanese works which can be based on official products or completely original creations. Such products are sold online on specialized sites, on the authors' own sites, and at conventions such as Comiket and the audio-focused M3.