Saga is originally an Old Norse word meaning “story” or “epic tale”. It has immigrated into English by way of The Icelandic Sagas, which were first translated into English in the 19th century.Etymology ramble Since then, “saga” in English has the meaning of a long, epic story, sometimes with the subtext “long-winded”. Titles containing "Saga" most often come in the format "(The) X Saga" (the article is optional). X is sometimes the protagonist, but can be practically anything — though usually a proper name or a noun. “Saga” is simply attached at the end, treating the whole title as a compound term. In the original Norse sagas, there was always a genitive case involved — mostly of the type "<Protagonist's> saga" or "Saga of <the protagonists>". A third, rare variant is "(The) <adjective> Saga" (not always clearly distinguishable from the first type). This kind of title usually lampshades that the work is a series of more-than-average length and/or has a considerable number of instalments.
Examples of the The X Saga type:Anime and Manga
Examples of other types (with genitive or adjectives):Literature