A Companion is a skilled, well-educated and well-respected member of a guild of professional courtesans/entertainers, somewhat similar to oiran. While they do frequently engage in a form of state-sanctioned prostitution, they are nonetheless treated with a great deal of respect and deference from nearly everyone (as seen in several episodes, including "The Train Job"), though non-guild prostitutes (as seen in the Firefly episode "Heart of Gold") are generally treated in the reverse, even if they are former Guild members.

Inara Serra, one of the central protagonists of Firefly, is a licensed Companion, and Companions, the nature of the Companion profession, and the Guild, all feature prominently in the series.

Registered Companions are culturally well-educated with training in a number of areas, including psychology (as indicated by the exchange between Inara and Saffron, and comments from Inara later in the episode as well, in "Our Mrs. Reynolds"), music (as mentioned by Nandi in "Heart of Gold"), fencing (as seen in the episode "Shindig"), and languages, as well as unarmed martial arts (indicated in the film Serenity)

As revealed in material from the Serenity DVD and from the shooting script featured in Serenity: The Official Visual Companion, in the "core" planets they are typically trained from a very young age.[1]

Relatively little is known about the Companion Guild's rules and practices, or the customs of Companions, though a few details have been revealed or implied in various Firefly episodes:

A Companion is allowed to choose her own clients (stated by Inara to Kaylee in the Firefly episode "Serenity", and shown as Inara goes through her messages on her shuttle's touch-screen computer in "Shindig").

A Companion is allowed to take clients of the same sex as herself (as shown in "War Stories")

A Companion must have a yearly physical examination in order to keep her license (as seen in the episode "Ariel").

A customer who behaves badly enough can receive a "black mark in the Companion registry," after which no registered Companion will contract with them (mentioned by Inara in the episode "Shindig").

A form of tea ceremony is a part of the traditional opening to a meeting between a Companion and her client (featured in the episode "Jaynestown").

A Companion frequently provides a form of psychotherapy for her clients (also seen in "Jaynestown")

Trainees on border planets seem to begin their training at an older age than those on the "core" planets (as mentioned in the original shooting script and deleted scenes for the feature film Serenity; Inara says of the trainees and her own training that "[Inara] started [her] training at twelve").[1]

Trainees come from good families and the training houses have high academic standards.

While the Companion Guild is in many ways a working company of skilled artisans, it also would appear to be a kind of religious sect. Heads of Companion houses are called "priestesses", and Inara's house is called "Madrassa", a term for an Islamic religious school. There are heavy religious overtones to many Guild practices, such as the use of incense, a focus on contemplation, and a cloistered lifestyle.

As mentioned above, Inara Serra is a licensed Companion. However, she is not the only character to be featured in the series who is, was, or received training to become a Companion. Although most are not currently licensed Companions, several minor characters are known or thought to have received Companion training:

Nandi, featured in the episode "Heart of Gold", was trained as a Companion. During her training, after a stressful incident with a dulcimer, she chose to strike out on her own outside of the Guild's sway and took control of a whorehouse on a border planet.

The femme fatale (her true name is unknown, though she is known by several aliases throughout the show, including Saffron) featured in the episodes "Our Mrs. Reynolds" and "Trash" was firmly thought by Inara to have received Companion training.

Several background characters at the Companion Training House in Serenity are, of course, in training to become Companions, and at least one older woman at the house (Sheydra), a teacher of theirs, is likely a registered Companion as well.