In the Mass Effect games, many familiar sci-fi tropes are explored, ranging from faster-than-light travel to first contact with advanced aliens and galactic politics. There is also the theme of robots wondering how to be human.
Already, science fiction has explored this theme with the likes of Lieutenant-Commander Data of the Enterprise, and the Mass Effect games brought this trope to life with EDI, a rare and powerful AI that wants to discover its (or maybe her?) own humanity. EDI faces a difficult road, but the reward is impossible to resist.
Born A Servant
In this science fiction universe, virtual intelligences are common and are used as tour guides, combat calculators aboard battleships, personal secretaries and more. But a true AI is forbidden, like in the Dune universe. True AIs are widely feared as having the potential to overpower their organic creators. The Geth proved this when they turned on the Quarian people 300 years ago (but as Shepard found out later, the uprising was largely justified). Humanity produced VIs like any other race, and the Systems Alliance had a powerful VI on a military base on Earth's moon as of 2183. That system went rogue, and Shepard had to shut it down before the now-self-aware VI went on a destructive rampage. Shepard called it "mission complete" and moved on, but the Commander and that VI would meet again.
That VI would end up in the hands of Cerberus, the shady pro-human cabal, and the Illusive Man made sure to make the most of its potential. The Illusive Man isn't the type to respect boundaries or limits of ethics or science; he wants to unlock potential anywhere he can find it, no matter what kind of controversy he stirs up. This often strained his relationship with Commander Shepard, but EDI acted as a fine bridge between them. Shepard was wary when EDI, a true AI, was placed in the Normandy SR-2, as was Joker, the pilot. EDI proved itself compliant and very helpful in the battle against the Collectors, and it was "shackled" to prevent any accidents. When the Collectors ambushed the Normandy and captured the entire crew, Joker manually freed EDI, and it became even more autonomous and self-aware than ever before.
By this point, Joker and Shepard considered EDI a "she" rather than an "it" (based on EDI's female voice), and EDI had formed strong "feelings" of attachment and loyalty to her crew. When Shepard broke away from the Illusive Man and Cerberus, EDI followed the Commander, leaving her creators far behind. By now, EDI had it all: freedom, friends, autonomy and a unique personality. She wouldn't let Cerberus take all that away.
The Machine Heart
In 2186, as the Reapers invaded the galaxy in force, EDI proved once again to be a hero for freedom. She was now affiliated with the Systems Alliance through Shepard and Joker (hiding her true AI nature from Alliance officials). She strongly opposed the Reapers, despite being a machine like they are. Like the Krogan people, EDI wanted to build her own future, rather than receive a future from another party (complete with strings attached). EDI even installed herself in a synthetic body that Shepard had captured from Cerberus on Mars, allowing her to pick up a gun and fight the forces of evil personally.
Along the way, EDI began to explore what she perceived as her humanity and modified her core programming to reflect that. She reprogrammed herself to make self-sacrifices and put the needs of others above her own, and she stated her willingness to die for her crew (something the Reapers wouldn't understand). EDI and Joker slowly formed what was first a friendship, then what looked like romantic involvement. Both of them knew that this was a wild new frontier in personal relationships, social sciences and philosophy, and no one, not even EDI, knew if this was true love or not. Commander Shepard, depending on the player, will either support the relationship or not. EDI and Joker can become a proper couple, bonding over their shared interest of spaceships and humor.
Not everyone is thrilled about this. Javik, the Prothean soldier from a previous era, hates all synthetics and AI, based on the experiences of his own cycle. He denies the idea of EDI having emotions, free will or human rights and sees her only as a tool that is going through the motions. EDI feels differently, and the two parties are at a stalemate. It's possible that deep down, EDI is afraid that Javik is right; is she really just imitating love and free will? If she harbors any doubts, she won't let the AI-hating Prothean get clued in, keeping a stern poker face around Javik. No one can keep secrets better than a robot, so Shepard will have to trust EDI that she is exploring this scary but thrilling new frontier the right way.