Intercepting Seg-El in the street, Adam Strange gave Seg the sunstone. Seg later returned home, showing it to his parents. They offered to hold it for him, as the symbol was outlawed. He agreed, but instead stole it. Walking home late sometime later, a member of Sagitari searched Seg, finding the sunstone. He knocked them down, taking the sunstone. He was quickly found by his mother in a skimmer, which they used to travel to his grandfather's Fortress of Solitude. Arriving there, Seg used the sunstone to unlock the Fortress.
"Light-Years From Home"
Finding himself in the Phantom Zone, a "hallucination" of Val-El explained to Seg-El that the sunstone could be used as a gateway back into the real world via one of numerous wormholes, as it contains the "harnessed energy of a 10 billion year old yellow sun". After opening a portal, the "hallucination" reshaped into the form of Brainiac, having tricked Seg-El into returning them both to the real world.