From Dragonball Online Wikipedia
Dragon Ball Online takes place on Earth, 216 years after the events at the conclusion of the Dragon Ball manga series. The villians in Dragonball Online is an evil organisation known as the Dark Eye. The Dark Eye are time meddlers who are changing the events of the past. The members of Dark Eye are under the effects of mind control. Mind controlled victims are characterized by a green gem marked with an "X" that rests in their forehead. The Mastermind behind the Dark Eye Organisation is currently unknown.
You play as a character who is trying to repair the 'Cracks in Time' created by the Dark Eye. Time Petrol Trunks helps you travel through time so you can repair Time Cracks. Throughout the game you'll find similar cracks in time all over the world and must travel through them into the past to preserve the Earth's history. All events which take place in Age 1000 take place on Earth.
The story of Dragonball Online is a sequel to that of the manga "Dragonball" (the animes Dragonball & Dragonball Z) written by Akira Toriyama. Toriyama has creative control over the game and any events from the movies or anime that were not based on his manga will be, more or less, ignored.
Game Prologue Translation
A long time ago there were mysterious wish giving marbles, the Dragonballs. There was also a child, Goku, that sought after the Dragonballs.
Through Goku's many adventures the confrontations he faced grew, but with the help of the Dragonballs the earth was saved from crisis.
200 Years since age 777, when justice was brought to Majin Buu, the earth has enjoyed peace and change.
Goku and his allies have left and on the earth, along with the humans, the children of Majin Buu, known for their mystical powers, have began to spread. Namekian adults, who've lost their homeland, have migrated to Earth.
Now, in age 1000, it is a peaceful era of well-being.
Suddenly, pale-faced invaders threaten the future of Earth. They come in a time machine from the unknown and endanger the Earth's past. These men are beginning to take away the lives of people.
With the universe threatened the time patrollers have given chase through the cracks in time.
An accidental time portal has opened.
Children have entered into it and passed through
it's twisted construction where there is no return.