Tamatebako

The Tamatebako is a box that has the powers to make anyone grow older, and is rumored to be in the possession of Ryugu Kingdom. Vander Decken IX decided to use the box to make a young Shirahoshi older in order to have her age match his and marry her. The box is not yet seen in the series, but was first mentioned in Jinbe's flashback in Chapter 626.

Trivia

 * The Tamatebako is an origami model that derives from the mystical box in the legend of Urashima Taro, 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 the age that Otohime stored inside the box; Urashima instantly grew to be a 300 years old man.