In December 2499, Private Sejak was a marine assigned to Third Squad, 417th Confederate Marine Platoon. The platoon was deployed to Mar Sara to retrieve a piece of Confederate equipment. Third Squad was chosen to spearhead the recon of Oasis.
Sejak was the youngest member of the platoon, mostly likely in his teens. He became increasingly agitated during the engagement with the zerg at Oasis and did not survive to return to Bunker Complex 3847 with the remnants of the platoon, either being killed in the battle or during the retreat.