الحلقة 551 - العودة إلى الخط الكبير! معركة لوفي النهائية مع البحرية

Episode 551
The Return to the Grand Line! Luffy’s Final Battle with the Marines
Japanese: グランドラインへの帰還！ルフィの海軍との最後の戦い
Gurando Rain e no Kikan! Rufi no Kaigun to no Saigo no Tatakai

The crew navigates through the mysterious island's puzzles, which are tied to an ancient civilization. They uncover a hidden chamber with a map that reveals more about the Grand Line's past and the true treasure. However, they are ambushed by a group of powerful pirates who also seek the treasure, leading to a dramatic confrontation.