Other source:

Tienshinhan, Krillin, and Yamcha continue to train at Kame House. Simultaneously, Kami and Mr. Popo send Goku on a special training mission to fetch a crown. As Goku tries to take the crown from the top of a mountain, he is struck by lightning. Goku meets a young girl who uses her “sixth sense” to find her lost bird. This makes Goku realize how he must acquire the crown: he must be faster than lightning.