Dragon Ball GT: Goku Gaiden! Yuuki no Akashi wa Suushinchuu

ドラゴンボールGT 悟空外伝! 勇気の証しは四星球(スーシンチュウ)

Years after the end of the Dragonball GT, the story continues in this special with Son Goku's now eldery granddaughter Pan, and a new generation of super saiyajins, the great-great-grandsons of Goku and Vegeta

100 years after the end of DBGT, all the heroes of Earth have died...except for Pan, the granddaughter of Son Goku. Pan has a grandchild named Goku Jr. However, he does not have the bravery of his great-great-grandfather. Pan suffurs a heart attack, and Goku Jr. believes that he might be able to save her with the power of the 4 star Dragon Ball. Along with the school bully, he tries to find the ball...and unleashes his hidden bravery and power.

(Source: Anime News Network)