Supporting characters are characters who are actively involved in the life of your primary cast, but who you have no interest in actively role playing. Supporting characters may be present within threads, but should always take a background role and not be the primary participant or focus. Likewise, supporting characters should not be played in the public ICC, although they may appear.
They might be parents, current or former romantic partners, children, or co-workers. As long as they have a presence in your character's life currently, you can set them up as a supporting character. Supporting characters should be placed in the 'Relationships' section of the character sheet of your characters who they are intended to interact with.
Supporting characters use the following template, taken from the primary character sheet—with a slight modification:
Name:
Age:
Gender:
Species:
Occupation:
Appearance:
Personality:
Abilities:
Situation:
Adoptable:
The 'Adoptable' field on the supporting cast template is a binary yes/no field. If you would like the possibility of another player portraying this character in a more active role, then you may mark the field as 'yes.' Otherwise, mark it as 'no.' If someone wishes to play a member of your supporting cast who is available for adoption, they may talk to you about it and—assuming you both agree—create the character as they would with any normal primary character.