While this game kicks ass, the story doesn't. I want to fix that.
You are an Outer, a human who is unaffected by the Femto energy that was unleashed during the first Moonfall. A chunk of the moon broke off and crashed into Earth, reddening the sky and poisoning the seas. Many people died, and to make matters worse, Femto corrupted many Artificial Intelligence units, causing them to break free of human control and take over military technology. Each AI has its own personality and operates under their own faction, the Immortals.
As a result of this war, humans forced to take refuge under the protection of Consortiums, like corporations that also rule their own countries. The Consortiums are Horizon, Orbital, Zen, and Sky Union, and they all need to abide by the rules of treaties made post-Moonfall. That doesn't mean that they don't try to aid each other in desperate times of need, but one Consortium is always looking for repayment from another when they do help out.
Outers like yourself are contracted by Consortiums as Reclaimers to fight off the Immortal threat through the use of Arsenals, massive mech suits that are armed to the teeth with weaponry. Outers are implanted with neural links to their Arsenals, and then those Outers are registered as Reclaimers. You can go it alone, but most Reclaimers join groups like Bullet Works and Panzer Crown, but they usually have a theme they try to stick with. The Western VII is made up of convicts trying to reduce their sentences, Panzer Crown is an all-female group, Immortal Innocence is made up of younger Reclaimers that have all made it out of some really hairy situations relatively unscathed, etc.
You all will be joining the group Iron Dragons, a relatively new group in desperate need of some new members.