The story goes a little like this - there's an advanced society that lives in a city called Thera. Outside the border of the city lies a vast wasteland inhabited by people who are not of Therian blood and are not allowed to enter the city. You play the same linear story through two viewpoints - a female character from inside the city, and a male character from outside. 

Your journey(s) revolve around an experimental biological weapon. This device merges with its host to provide them with tools, virtual storage, and physical and mental modifications/upgrades. 

In short, you (both characters) wind up with one. Pretty cool, right? 
But there's a catch. 
They're killing you both slowly, and the Therian government wants them. You're simultaneously on the search for a cure to save yourselves while also highly wanted criminals running from the government for "stealing" a top-secret weapon. 

As you carry on with this search, you begin to uncover the backstories of the characters you play as, you will meet an assortment of characters who join your team, and you slowly discover who the Therian government really is. You learn that the weapon that's killing you is a stolen experiment and there are many more dangerous experiments just like it out there.