The events of Dragon Ball Online take place in the age 1000 (216 years after the Buu saga.) with the role of villain going to a group headed by Mira. Mira originates from the Demon Realm and is attempting to invade the Earth in the age 2000, with the help of Frieza's army and the Red Ribbon Army, but currently has his eyes set on the past by way of time travel. The purpose for him wanting to go back in time is so that he can attempt to obtain Goku's DNA which he will then use to strengthen himself for when he invades the Earth in the future. Currently, all known henchmen of the Dark Eye have been under the effect of mind control. Mind controlled victims are characterized by a green gem marked with an "X" that rests in their forehead (in some cases it may be in their chest or could also be a mask instead of a gem).
The player takes the role of a character from an unknown time period who is sucked through a crack in time caused by Mira's Army. Eventually, the player makes their way to the age 1000 (with the help of the Time Patrol Capsule and Trunks) and throughout the game the player will be able to travel through different time periods to alter the past and fix the present.
It should also be noted that all of the events that the player witnesses in the Age 1000 currently only take place on the planet Earth. Both the Majin and Namekian race start their journeys, just like the Humans, on Earth. The new planet Namek was destroyed by Mira in the age 853 and sections of the Earth have since been transformed to resemble the planet Namek.