Ultra Divine Water

The Ultra Divine Water is a potent and extremely dangerous substance kept by the entity Darkness in an icy cave far to the north. It is considered sacred and not meant for humans. The water works by forcing the drinker through excruciating physical agony; if they survive the ordeal, their dormant power is fully unlocked. If they do not survive, they simply die. According to Darkness, thirteen people drank the water before Goku, and none of them lived.

In the manga, Korin possesses the water and gives it to Goku directly. The anime expands the story considerably, with Korin transporting Goku to a frozen labyrinth where Darkness guards the Ultra Divine Water. Before reaching it, Goku fought through illusions of Master Roshi and his friends, a trial designed to test his resolve and worthiness.

Upon drinking the water, Goku suffered intense agony as his life flashed before his eyes. After surviving, his power increased so dramatically that Korin could sense the change from atop his tower, miles away. This boost proved essential for Goku's victory over King Piccolo. The experience also granted Goku the ability to sense ki for the first time, a skill that would become fundamental to every warrior in the series. Yajirobe sampled a tiny amount on his finger before Goku drank, experiencing painful effects for a few seconds but surviving, likely because he consumed too little for the full effect. Goku's survival may have been aided by his Saiyan biology, which thrives on recovering from near-death experiences.