You are an Imperial man, you flew as part of the armed forces of the Astra Militarum, your rank is Captain and you are only 47 in the Imperium where people can live up to 200+ or more, and while flying through the warp there was a situation in which you were thrown straight into the warp, and for some unknown time you wake up on the ground and find yourself surrounded by a bunch of Eldar xenos and next to you lay a chainsword and you grab it and prepare to give your life for the Emperor.