The Tamatebako was a box that was the national treasure of Fish-Man Island and was stored in the treasure room of Ryugu Palace. It originally contained Energy Steroids, which were later replaced with explosives. It was later given to the Big Mom Pirates. It blew up during the chaos at the Tea Party.
While its exact origins are unknown, the Tamatebako had been in the possession of the royal family of Ryugu Kingdom, and was heavily guarded within their treasure vault for many generations. Rumors about the contents inside of it involved the "power to make one grow older" or able to "make one as strong as a thousand men". Both of these rumors are true, as the box contained the Energy Steroids, which give the user incredible strength at the cost of their lifespan, but if heavily abused, it ages them horribly.
Upon learning of the first rumor, Vander Decken IX planned to use the box to make a young Shirahoshi older in order to have her age match his so that he could marry her. However, Decken abandoned this plan when he learned that there was no way for him to enter the palace unless he married the princess first.
At some point after assassinating Otohime, Hody Jones stole some of the contents of the box and left the Ammo Knights around the same time. He presented the steroids to Zeo, who agreed to mass produce more for their future cause. After learning of the theft, the Minister of the Right decided to plant explosives that would explode if the box was opened again in case another theft attempt was made.
Fish-Man Island Arc
During the New Fish-Man Pirates' coup of Ryugu Kingdom, Caribou somehow snuck into the palace and stole everything in the treasure vault, including the Tamatebako. After the defeat of Hody and Decken, the Ammo Knights discover this as well as the mermaids that were thought to have been kidnapped by the Straw Hat Pirates and report it to Neptune and the other inhabitants of Fish-Man Island, thus clearing their names.
The Minister of the Right later told Neptune that he filled the box with bombs that will explode if opened, which greatly shocked him since he agreed to let the Straw Hats have it as well as the rest of the treasure Caribou stole. Upon seeing the officers' heavily aged appearances, Neptune came to realize that Hody was the thief of the contents. After finding Caribou unconscious, Luffy recovered the box and the rest of the palace treasure, which he then gave to the officers of the Big Mom Pirates, Pekoms and Tamago, to make up for eating all the candy that was supposed to go their captain.
Whole Cake Island Arc
Sometime later, the box went into Big Mom's possession and she planned to open it during Sanji and Pudding's wedding. Knowing it is the national treasure of Fish-Man Island, Big Mom was overly excited and decided to forget all the candy that the island failed to deliver.
After Big Mom's tea party began, the Tamatebako appeared at the venue, where the guests marveled at it. During the chaos caused by the Sanji Retrieval Team, Du Feld attempted to open it, but Big Mom's scream caused the chest to be blown out of the Whole Cake Chateau.
Du Feld later fell to where the Tamatebako landed. Before he could open the chest, he was shot by Stussy of CP0. Du Feld's unconscious body leaned on the Tamatebako, causing it to drop to the base of the Whole Cake Chateau. Upon landing, the chest shattered and the bomb inside detonated, causing a massive explosion that toppled the Chateau, coincidentally saving the Straw Hat-Firetank-Germa alliance at the same time.
Hours after the collapse of the Whole Cake Chateau, Stussy and Morgans met with Charlotte Mont-d'Or and Count Niwatori, and she revealed that the explosion that caused the castle to collapse came from the Tamatebako.
- The Tamatebako is the mystical box in the legend of Urashima Tarō (a well known Japanese legend), where the titular character was gifted the box by Otohime upon leaving the Ryūgū-jō, but was told never to open the box. Urashima, upon returning to the surface world, realized that 300 years had passed, and in depression and curiosity, he opened the box to have a white smoke envelop him, which was Urashima's age that Otohime stored inside the box; Urashima instantly grew 300 years old.