A very large proportion of drawn work is derivative: characters somebody else created, in situations their creators did not write. Legally this occupies uncertain ground that varies by jurisdiction. Socially it runs on a fairly stable set of conventions that no one wrote down, and those conventions are what actually govern behaviour most of the time.

Knowing them matters practically, because breaking them produces community consequences much faster than legal ones, and community consequences are what most people in this area actually encounter.

The commercialisation line

The most widely observed norm concerns money. Sharing derivative work freely is generally accepted; selling it is more contested; mass-producing merchandise from it is contested strongly. The gradient is roughly proportional to how much the activity looks like competing with the rights holder.

Where selling happens, the convention is usually small scale and limited runs, often at events. That practice has decades of precedent behind it in some traditions and none in others, which is one reason arguments about it are so persistent.

The visibility line

The second norm concerns not putting the work in front of people who did not seek it, and particularly not in front of the original creators. Sending explicit derivative work to the person who created the characters is universally regarded as a serious breach, and it is one of the few things nearly every community agrees on.

This connects to the tagging and routing argument in the piece on how tags decide who sees a page. Correct labelling is partly a technical matter and partly this norm expressed in metadata.

Tolerance is not permission

Many rights holders tolerate derivative work because it is good for their property, and some actively encourage it. Tolerance can be withdrawn, is frequently withdrawn selectively, and does not create any right that survives a change of ownership or of policy.

Practically that means a body of work built entirely on somebody else's characters is exposed in a way original work is not. That is one of the arguments for building original characters made in the piece on where the money comes from, since licensing requires ownership.

Norms differ between communities

What is unremarkable in one tradition is unacceptable in another. Conventions around selling, around explicit content involving particular characters, and around how work is credited vary substantially between countries and between fandoms of different eras.

Assuming your own community's norms are universal is the commonest way people cause offence without intending to. The safer approach is to observe how established participants behave before publishing, which takes an evening and prevents most problems.

Credit within derivative work

Norms about crediting the original are strong: naming the source work is expected, and presenting derivative characters as your own creations is regarded poorly. That is separate from the artist-credit question in the piece on artist credit, which concerns credit for the drawing rather than for the characters.

Both matter and they are frequently confused. A derivative piece has two credits to carry: the source of the characters and the maker of the image, and stripping either one is a distinct failure.

When norms and law disagree

They frequently do, in both directions. Some widely accepted practices have no legal protection, and some legally defensible ones are socially unacceptable. Neither system overrides the other in practice, since they operate through different mechanisms with different consequences.

The workable position is to satisfy both where possible and to be aware which one you are relying on when they conflict. Confusing what is legal with what is accepted is how people end up surprised by the reaction to something they were confident about.

Anonymity is the last convention worth naming, and it cuts both ways. Working under a pen name is normal here and it is treated as ordinary rather than as evasion, but it also means a reputation cannot be transferred and that the same person may hold several unconnected bodies of work. Communities generally respect the separation and treat linking two identities without permission as a serious breach.

Working within conventions nobody wrote down

Observe how established participants behave, keep commercialisation modest and clearly labelled, never put work in front of the original creators, credit both the source and the artist, and remember that tolerance can end. That covers the conventions that actually govern this area.

Characters here are fictional and unmistakably adult, and real-person likeness is never used, as set out in the reader agreement.