''[[http://forums.spacebattles.com/threads/blood-and-fire-a-mass-effect-halo-fusion.215185/ Blood and Fire]]'' by Tavi is a ''VideoGame/{{Halo}}[=/=]Franchise/MassEffect'' FusionFic.

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. When Covenant forces attack the human colony of Eden Prime, a combined team of humans and Citadel races is deployed as reinforcements. Things get more complicated fast when it turns out there's more than meets the eye...

!This fanfic contains examples of the following:

* AllYourBaseAreBelongToUs: [[spoiler: Saren sabotages the Spectre quarters.]]
* AlternateUniverse: Humanity being on much better terms with the Citadel. Garrus already a Spectre trainee. Tali on the Normandy's shakedown. Quarians and Krogan getting a better deal from the Council. [[spoiler: Ashley is an officer and N5.]]
* ArmorPiercingAttack: Covenant plasma weapons deal electrical and thermal damage that kinetic barriers cannot protect against.
* AnArmAndALeg: Nihlus loses a hand to [[spoiler: Saren's treacherous attack on Spectre headquarters.]]
* AwesomeButImpractical: The original Spartan programme was just too costly despite the extreme quality products, such as augmentations still unrivaled after 50 years. WordOfGod directly states that the cost of equipping and training one Spartan matches that of a mechanized company. Its replacement, the N7 Programme, is more economical without losing too much effectiveness.
* BeCarefulWhatYouWishFor: The Batarians [[spoiler: wanted to be isolated? They got just that. To be specific, once they were defeated by the Alliance, the only relays into and out of their space are now blockaded at all times. Anyone who tries to enter or leave is obliterated.]]
* CarFu: [[spoiler: Ashley ramming a Hunter with a hover truck.]]
* TheCavalry: Humanity is introduced to the Citadel races via the latter doing this.
* CompositeCharacter: Shepard's origin combines several of the canon backgrounds.
* DepletedPhlebotinumShells: While the Covenant plasma is better in a straight fight, special effects on mass accelerator rounds have their own utility and are available even on starship guns all the way up to dreadnought size.
* DoomedByCanon: Averted with [[spoiler: Nihlus and Jenkins.]]
* EstablishingCharacterMoment: InUniverse for Tali. "Tali, Nihlus wouldn’t drag you across half the galaxy if you weren’t up to this. You introduced yourself to us by throwing a grenade at a crooked info-broker!"
* FourStarBadass: The Spartans we've seen so far, including John, Linda and Kelly.
* FusionFic: The author avoids several problems with the matchup, most obviously the power level gap, by doing this. Rather than using the Covenant wholesale in their original Halo form, the Covenant here are an advanced faction with Geth- or Collector-level grasp of the Mass Effect, enabling them to keep their energy weapons without grossly overpowering the Citadel races. Similarly, the object of their religious worship is changed to the Protheans, who they consider Forerunner, rather than Halo-canon Forerunners who would utterly destroy the Reapers in a straight fight.
* HigherTechSpecies: The Covenant have a tech advantage over the Citadel races, with this being balanced out by personnel numbers.
* HumanityIsInfectious: 'Where the hell had [Garrus] heard that? Damn human memes.'
* MagicKnight: The Covenant have their own biotic combatants. WordOfGod directly equates Zealots with Krogan Battlemasters.
* MythologyGag: '[Jacob Keyes] made a mental note to find out who had told the cranky old Turian about air quotes. There was going to be hell to pay for that one.'
* RequiredSecondaryPowers: The Citadel races know the science behind Covenant plasma weapons, but they lack the material science and power generation knowledge to make the things work in a practical, combat-useful package rather than in the laboratory.
* ShoutOut:
** Shepard mentions talking to a psychologist named Doyle Resch. Dr. Resch is from ''Fanfic/BruceHasAProblem'', where he's a psychologist working at Arkham Asylum and is better known as "Doc Ironballs."
* TitleDrop: "Every turning point in [Shepard's] life has involved two things doctor. Blood and fire."