Shatterstar is the child of the Earth mutant Allison Blaire, alias Dazzler, and the artificially engineered biped Longshot, from the dimension known as the Mojoverse.
He was born sometime after the fall of Mojo, and was delivered by a time-traveling Rictor and his future self, the present day Shatterstar body Ben Russell, soul Gaveedra-Seven.
As part of a temporal loop, Shatterstar used Arize's machinery to ensure his parents did not remember his birth, and then transported his infant self where he needed to be. X-Men (2nd series) #11, X-Factor (1st series) #259
Young Shatterstar was next seen as an adult, 100 years in the future, rebelling against the rule of the tyrannical Mojo V.
At this point in his life, Shatterstar apparently believed himself to be one of the artificially engineered bipeds of the Wildways, the slave race of Longshot who turned against Mojo and the Spineless Ones. Shatterstar lived on the run in the shadows for two years before joining the Cadre Alliance.
The Alliance's efforts in Shatterstar's time were no more effective than those of Longshot a century prior against the original Mojo.
Desperate for aid, Alliance scientists and mystics constructed an elsewhen transporter to send a representative through time and space in order to recruit the legendary X-Men from Earth, to join them in their fight.
Shatterstar volunteered to be the representative and crash-materialized 100 years in the past in the X-Mansion's underground Danger Room. New Mutants (1st series) #99
Shatterstar appears for the first time, in a silent, one-panel cameo at the end of the issue (a la Cable's cameo appearance in New Mutants #86). He'll receive a proper introduction next issue, though it's worth noting that here, he has two long blades extending out of his hand, not unlike Wolverine's claws, while next issue (and thereafter) he wields an actual sword he holds in his hand.
The X-Men were off-world at the time, but Cable and his band of New Mutants were in residence to greet Shatterstar. Suddenly thrust into battle with the Danger Room's attack drones, Shatterstar was in no mood to quietly explain his position to the New Mutants when they entered and had to be beaten unconscious by Cable in order to calm him down. While he was recovering, however, dog-soldiers from Mojo's Imperial Protectorate locked onto Shatterstar's transport signal and followed him to the present time and local space. Shortly after Shatterstar revived and related his story to Cable's team, they were attacked by the legion of dog-soldiers. During the battle, Shatterstar demonstrated his commitment to winning at all costs when a dog-soldier grabbed him from behind and Shatterstar stabbed himself through his own abdomen in order to penetrate the construct warrior behind him.
The Protectorate soldiers were defeated, but Shatterstar's elsewhen technology was damaged in the mêlée, leaving him trapped as an exile on Earth. He and Cable reached an agreement: Shatterstar would join the newly-minted X-Force strike team for the present, lending his swords and skill to the fight for Xavier's dream, in exchange for Cable's promise to one day return with him to Mojoworld and overthrow the reign of Mojo V. New Mutants (1st series) #100