Blood and Fire by Tavi is a Halo/Mass Effect Fusion Fic. The Citadel races have long been involved in a cold-again, hot-again war with the Covenant, a technologically advanced but numerically inferior theocratic empire. When they attack Shanxi, a colony belonging to the newly encountered race known as "humanity", the Citadel comes to the rescue with offers of assistance to the newcomers, who gladly accept. Fast forward several decades. Covenant forces attack the human colony of Eden Prime...