"Seiun", the Japanese word for "nebula", was taken from the first professional science fiction magazine in Japan, which had a short run in 1954.

It is similar to the Hugo Award, which is presented by the members of the World Science Fiction Society, in that all of the members of the presenting convention are eligible to participate in the selection process, though it is not a one-on-one comparison as the Hugo Awards are open to works from anywhere in any language, while the Seiun is implicitly limited to works released in Japan and written in or translated to Japanese.

A professional work or achievement which appeared for the first time in the previous calendar year may be considered eligible.

There are no written rules about word count for literary fiction categories, so that the decision of eligibility in that regard is left up to the voters.

With consideration for voters' availability, a work which appears in a magazine (such as a part of serialized works or short story) or released as audio-visual media (such as a TV show or film) but wasn't chosen for the reference nominee lists may be eligible again if published as a book or released in any other media format.