Short-Term Focused Cover Page Serials (短期集中表紙連載,Tanki Shūchū Hyōshi Rensai?), usually shortened to Cover Stories or Cover Arcs, are a series of supplemental stories told through the cover pages of select chapters. With few exceptions, they focus on the activities of various antagonists and side-characters after their initial encounters with the Straw Hat Pirates.
Though easily overlooked, cover arcs are as canonical as the manga proper, many having introduced or explained elements pivotal to the main storyline—e.g.Vice-Admiral Garp.
(It should be noted that, despite similar—sometimes identical—construction, cover arcs are distinct from the Where They Are Now series, which follow a different numbering.)
Cover arcs follow a simpler, more disjointed storytelling format than the manga proper; their pages are never subdivided into panels, and their few speech bubbles always use either pictograms or simple words in English. Each installment delivers the majority of its dialogue and narration in a page-bottom caption, which also gives the installment's number in the overall arc.
(The first installment of a cover arc will typically be captioned as "Cover Arc Number [X]", saving the arc's official name for the second installment on. Reflecting this, most cover arcs keep their protagonists obscured (or outright hidden) in the first installment, effectively challenging readers to predict their identity from context clues.)
By Eiichiro Oda's official count, there have been twenty-four cover arcs thus far.
Apart from these, the anime has faithfully adapted the cover stories' aftereffects whenever they appear in the main storyline —e.g.Hatchan returning in the Sabaody Archipelago Arc as a civilian chef—but never the stories themselves. At most, elements introduced by cover stories are given brief cameos, or else repurposed for anime-original material. The reasons for this remain unknown (notwithstanding fan theories that stories not focusing on the Straw Hat Pirates—and Luffy in particular—are commercially unpopular in Japan).
Currently, "From the Decks of the World" stands as the longest cover story overall, at 48 installments. "Caribou's Kehihihihi in the New World" stands as the longest with a single protagonist and plot, at 46.
Discounting the disparate pieces of the Straw Hat Separation Serial, "Wapol's Omnivorous Hurrah" is the shortest, at 23 installments.