One Piece Episode 221 , "The Mysterious Boy with the Whistle and Robin's Deduction!", begins a filler arc where a mysterious boy named Noko plays a melody that causes the Straw Hat crew to lose their memories of each other. The episode explores the chaos that ensues, as the crewmates revert to their past selves and forget their bonds, leaving only a calm Nico Robin, who was unaffected by the music, to deal with the situation.