A music-producing dojinshi circle from Hokkaido, Japan, consisting of 22 core members and multiple collaborators. IOSYS is best known for producing remix albums of music from the Touhou Project series of video games, which they have been doing since 2006 with over 90 albums to their name.

Their best-known works fall into the denpa category, with nonsensical high-pitched lyrics over catchy electronic beats, and feature memetic, Flash-animated music videos (For example, “Marisa Stole the Precious Thing”). However, they have also released instrumental, EDM, jazz, and rock albums.