Edge of Tomorrow AU
Humanity is at war with an alien race known as Mimics, and Lt. Col. Sam Winchester is an officer who has never seen a day of combat until he is unceremoniously demoted and then dropped—untrained and ill-equipped—into what amounts to little more than a suicide mission. Sam is killed within minutes, managing to take an Alpha down with him. But, impossibly, he awakens back at the beginning of the same hellish day, and is forced to fight and die again…and again. Direct physical contact with the alien has thrown him into a time loop—dooming him to live out the same brutal combat over and over.
But with each pass, Sam becomes tougher, smarter, and able to engage the Mimics with increasing skill, alongside Special Forces warrior and his brother Dean Winchester, who has killed more Mimics than anyone on Earth. As Sam and Dean take the fight to the aliens, each repeated battle becomes an opportunity to find the key to annihilating the alien invaders and saving the Earth.