The captain of the Freeden, a Vulture ship. He was once a Newtype pilot of the old United Nations Earth who piloted a Gundam X in the 7th Space War, and it was also him who fired the fatal shot which changed history. Now he searches the Earth for Newtypes to rescue and protect.

When one space colony declared its independence from the Earth Federation, the devastating 7th Space War, an all-out war between Earth and space, resulted. The Federation responded to the Space Revolutionary Army with mobile suits, called Gundams. However, the Space Revolutionary forces played their trump card and dropped hundreds of space colonies onto the Earth, plunging the planet into a seven-year-long nuclear winter. The Federation collapsed, but the Space Revolutionary Army was unable to invade the Earth in the aftermath of the colony drop. Fifteen years have passed. The year is now After War 0015, and a New Federation has sprung up on Earth to restore order. In space, the colonial leaders have been rebuilding their own forces as well. By chance, fifteen-year-old Garrod Ran has discovered an old Federation mobile suit, the Gundam X, and now he uses it to help out the Vulture ship Freeden in its struggle to keep the powers that be from repeating the mistakes of the past. 

The story takes place in unnamed timeline, where humanity has highly advanced technology. However, the human population is decreasing and it seems that they're on their way to extinction. 
The protagonists are Leos Alloy, Sthesia Awar and their Haro. They work on a Jupiter base called "Jupiter X", using "General Answer" (or "GA") which contains a massive repository of data about the alternate history of Humanity, Leos travels to the Earths' of the alternate timelines in an effort to collect data that might give them a hint for the evolution of mankind. 
(Source: Gundam Wikia)

Fifteen years ago, those living in Outer Space went to war with people still on Earth. During the battles of the 7th Space War, it was found that certain human beings had mysterious arcane abilities, powers of the mind to control and forsee. These gifted people were called Newtypes. They were valuable to both sides of the war; the Earth Federation designed the Flash System which allowed a Newtype pilot to control a horde of unmanned MS, called Bit-Mobile Suits.This was an effective weapon, but sacrificed the lives of many Newtypes. 
Space fought back for principal, believing the effect of living in Space heightened every human ability and eventually created the prized power of a Newtype, who was not something to use as a tool for war. But in the end, mankind was its own downfall. During the final battle, the Space Revolution Army (SRA) crashed numerous colonies into the planet Earth, with a devastating effect. 
Millions died as a result of the colony drop. Those that were fortunate enough to find refuge in a Shelter were both blessed and cursed; they wouldn't see the sun again for four years. The rest that made it through had to endure and suffer with living on a ruined planet, plagued by an endless winter and an ever-changing, chaotic atmosphere. With that, the war had ended. For now. But everyone who continued to live on was possessed by that tragic war, and the word "Newtype"... 
The year is After War 0015, and life on Earth is finally on its way to creating a more perfect world, except for the ruthless mercenaries who use mobile suits to make a living raiding; called Vultures, some of these people are merely chasing money, while others are running from the past. Enter 15 year old Garrod Ran, an orphan of the war. He is a lively and friendly boy who is trying to survive in the wake of the war, living off his daring-do's and knowledge of MS. Because of this, Garrod is hired to rescue a kidnapped girl from a Vulture ship, called the Freeden, and its stoic captain, Jamil Neate. 
But Garrod soon finds out that this job is entirely not what it seems; that the girl, Tiffa Adill, is actually a powerful Newtype, able to dream the future. And when Tiffa shows Garrod the Gundam X, Garrod can do nothing but bear witness to the suddenly changing times. He may learn that people's true intentions run far deeper, and that the Vultures and Captain Jamil Neate are their only hope for surviving the coming age, and the birth of the New Earth Federation. 
Must mankind repeat the tragic mistake of the past? 
 
Note: Includes the two-part one-shot "Kidou Shin Seiki Gundam X Gaiden: Newtype Senshi Jamil Neate"