Imposter Primarch: I Am the God Promised to Warhammer

[Warhammer + the Primarchs of the Lost Legions + causality + transmigration into 40K] A throwaway joke in a livestream comment, and he transmigrated against his will. One declaration, "I am X," and the impossible became true. Why did two Primarchs vanish? And why were all traces erased, while the original Space Marines were left alive? When Lin Zhao transmigrated into the Warhammer galaxy, he was lying under the barrel of a gun. At the last possible moment, he bet everything and claimed to be a remnant of this forbidden Legion. He had only meant to bluff his way to safety with a fake ancient oath, but his words kept aligning with the facts. Before transmigrating, he had been a lawyer who specialized in digging through history's dirty laundry. His whole life had been spent establishing a version of "the facts" that favored him, in gaps no one could bear witness to. Again and again, the "effects" he invented were proven to have plausible "causes." The Inquisitors wanted to burn him, so there would be no one left to put pen to paper; The Space Marines wanted to test his bloodline, only for genetic scans to find nothing at all; Even when a Primarch questioned him to his face, he could leave them speechless. A lie born of impersonation was believed by billions. Until one day, even the lie itself forgot it had ever been false. As the Imperium crumbled in flames, desperate humanity needed a god. Lin Zhao raised his head: "The one you want to return..." "I say he's back, and back he is."