is a
Japanese-language word meaning "
side story" or "tale", used to refer to an
anecdote or supplementary biography of a person. The use of
gaiden is commonly used in popular Japanese fiction to refer to a
spin-off of a previously published work that is neither officially considered a
sequel nor a
prequel. However, some
gaiden are retold stories in the perspective of a different character, similar to that of a
flashback.