Setting: Space age, faster than light travel to other system possible by various Mass Relays, floating creations in space that allow space craft to transverse systems. Various alien races are standard. As far as metaplot goes, the game is set after the attack by the Reaper on the citadel and two months after the death of Shepard on the Normandy.
In this case, Shepard sacrificed the council to rally to the defense of the citadel, and humans are almost universally considered usurpers. Also for the sake of lore, the Shepard in this timeline was male.
For information: Mass Effect Wiki
Players: 3 – 6
Character Types: Soldiers, Adepts (psychics - called Biotics), Engineers, Infiltrators
Races: Human, Asarii, Turian, Salarian, Krogan (See below)
Class Breakdown: Starting group will ideally have at least one soldier, adept and engineer.
Players
Cobalt
Mustang
Kosh
Potential Players
Sabre
Liltroll
Characters
Human Soldier (Cobalt)
Asarii Huntress (Mustang)
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Turian

Originally from the planet Palaven, turians are best known for their military role, particularly their contributions of soldiers andstarships to the Citadel Fleet. They are respected for their 'public service' ethic - it was the turians who first proposed creating C-Sec- but are sometimes seen as imperialist or rigid by other races. There is some animosity between turians and humans, largely due to the turian role in the First Contact War. This bitterness is slowly beginning to heal - shown by the cooperation of the two races on the construction of the SSV Normandy - but many turians still hate humans, and vice versa.
Salarian

The second species to join the Citadel, the salarians are warm-blooded amphibians with a hyperactive metabolism; salarians think fast, talk fast, and move fast. To salarians, other species seem sluggish and dull-witted, especially the elcor. Unfortunately, their metabolic speed leaves them with a relatively short lifespan; salarians over the age of 40 are a rarity.
Salarians are known for their observational capability and non-linear thinking. This manifests as an aptitude for research and espionage. They are constantly experimenting and inventing, and it is generally accepted that they always know more than they are letting on.
Asarii

A mono-gender race—distinctly feminine in appearance—the asari are known for their elegance, diplomacy, and biotic talent. Their millennia-long lifespan and unique physiology - allowing them to reproduce with a partner of any gender or species - give them a conservative but convivial attitude toward other races. The asari were instrumental in proposing and founding the Citadel Council, and have been at the heart of galactic society ever since.
Krogan

The krogan are a species of large reptilian bipeds native to the planet Tuchanka, a world known for its harsh environments, scarce resources, and overabundance of vicious predators. The krogan managed to not only survive on their unforgiving homeworld, but actually thrived in the extreme conditions. Unfortunately, as krogan society became more technologically advanced so did their weaponry.