saakuru サークル

In Japanese, a "circle," or saakuru サークル, is a group of people that share a same interest or hobby. There are two notable kinds: the circles that are school clubs, and the characters in anime join because they like a certain activity, and doujin 同人 circles, which publish anime-related stuff.

This is about the katakanization of "circle," which is used in a different way from English, i.e. it's wasei-eigo 和製英語. The word for a geometric "circle" in Japanese is maru 丸.

サークル活動

Since circles are made of people that share some kind of interest, it goes without saying that the "circle activities," saakuru katsudou サークル活動, the stuff the people in that circle do together, is based on that interest they all have in common.

For example, a music school club implies a circle of people with interest in music, learning to play instruments, and so on. One of their activities would be playing as a band.

同人サークル

Based on the idea above, within the doujin culture, a group of people that publishes a doujinshi 同人誌, or whatever other work, is called a "doujin circle," or doujin saakuru 同人サークル.

Basically, publishing a doujinshi is often an activity performed by multiple people collaborating with each other with the shared interested of making the thing real. That's why they're called circles.

個人サークル

A kojin saakuru 個人サークル, "individual circle," is the term given to a doujin circle composed of only one person.

If you think hard about it, it doesn't make sense, so avoid thinking hard about it.

Basically, the idea that a doujinshi is published by a circle that's composed of multiple artists and collaborators kind of stuck. So even if a doujinshi is published by a single person, it's still said to be a circle, even if it's a single-person circle.

Indeed, this contradicts the original meaning of the word "circle." Normally you don't call a group of one people a circle. This is only happens when talking about doujin circles.

Furthermore, since artists normally author things under fake names, or "pen names," pseudonyms, you end up with a situation where a single doujinshi author has two names: one for himself as an author, and one for his single-person circle.