A Mysterious Boy with a Horn and Robin's Deduction!

Robin walks the crew through her theory about the gaps in their memory, concluding that only those who drifted off to sleep were affected. The thief turns out to be a young boy who carries a low, droning horn, and the sound he produces is what drains people while they rest. Away from the ship, Nami has slipped off to a neighboring island, where she runs into that same boy after watching the locals brawl over a single newspaper dropped by a passing seagull.

Several characters relive their pasts as their lost recollections surface in fragments. Zoro remembers his rivalry with Kuina and the moment Koushirou handed him the Wado Ichimonji to carry her dream forward. Nami, bathing alone, puzzles over how she came to call these pirates her crew and why her old Arlong tattoo no longer makes sense to her. Later that night the boy perches on the Going Merry's figurehead and blows his horn, but Robin spots him and rouses everyone. When the child tries to cast another sleeping spell, Luffy charges him for sitting where he should not, takes a faceful of shimmering blue dust, and wakes with his memory restored.

This entry is entirely anime-original filler with no manga basis. The closing preview breaks from tradition: instead of Luffy proclaiming his goal of becoming Pirate King, an amnesiac Zoro cuts in with a threat to slice everyone down. Flashback appearances include Koushirou, Kuina, Bell-mere, Arlong, and the rest of the Arlong Pirates.