A cube of Katchin
Katchin (pronounced Cat-cheen) is a material said to be the strongest metal in the universe. In the English translation of the Dragon Ball manga, it is called Klangite.
Overview[]
Supreme Kai throws a block of Katchin to Goku
During the Majin Buu Saga, Supreme Kai used his powers of Magic Materialization to summon a block of Katchin to test the Z Sword. As Goku hurled the cube at Gohan, the Z Sword proved no match for the cube of Katchin, and thus the sacred Z Sword was broken, releasing Old Kai.
Video game appearances[]
In Dragon Ball Z: Buu's Fury, there is a wall made of Katchin in the Cave of the Ancients on Grand Kai's planet. Goku uses his Instant Transmission technique to pass the wall and get the ancient artifact hidden inside. Later in the game, Supreme Kai makes a block of Katchin appear in order to test the Z Sword like he did in the anime/manga.
In the Budokai series, one of the Supreme Kai's special attacks involves him summoning a block of Katchin and throwing it at his opponent (technique called Supernatural Abilities in Budokai 3). In the Budokai Tenkaichi series, the block is used in the basic rush of the Supreme Kai.
In Dragon Ball Online, it mentioned that the Groundbreaking Science article "Katchin Can Be Cut!" has an immense influence in the birth of the Swordsman class in the game.