1: Luffy's heart-wrenching decision to leave his crew behind

2: The tragic backstory of Nico Robin and the destruction of Ohara

3: Ace's devastating death in the war against Marineford

4: Sanji's emotional confrontation with his family in the Whole Cake Island arc

5: The heartbreaking separation of the Straw Hat crew at Sabaody Archipelago

6: Zoro's sacrifice and near-death experience at Thriller Bark

7: Nami's tragic past and her struggle to protect her village

8: Usopp's emotional departure from the crew and his journey to become stronger

9: The revelation of the Void Century and the true history of the world in the One Piece series.