Fanon / Mass Effect

• Female Shepard is commonly presented as the canonical version of Shepard in fan art and fanfiction, despite male Shepard being used in all of the promotional materials and statistics revealing 82% of players choose to play as him. This can be credited to the fact that women are overrepresented among the general population on fanfiction and fan art sites, while men are overrepresented among the general population in the player bases of third-person shooter (90+%) and western RP (75%+) games.
• Due to both male Shepard and female Shepard's individual voice actors being Canadian (and Bioware themselves being from Canada), an Earthborn-origin Shepard is thus assumed to be Canadian. Acknowledged in Mass Effect 3 where Shepard can offer to take his/her romance interest out drinking in what's left of Vancouver.
• A particularly popular theory on the ending of the series is that Shepard was actually indoctrinated from the point that s/he got hit with Harbinger's beam, with the final choices being whether or not Shepard successfully fights back or succumbs to the Reapers' influence.
• Certain artists commonly assume that for krogan, "the other two are internal," even though this is actually an urban legend invented by furry artist Narse when he forgot. The dreadfully uncomfortable shape of Wrex's codpiece would indicate both pairs are internal.
• Due to the clunky Mako controls in ME1, some fanfics have Shepard be a bad driver, with the squad have varying amounts of fear to Shepard's driving. This is kinda reinforced by a line Liara says in during the Lair of the Shadow Broker. After Mass Effect: Andromeda was released, the Fanon became that N7s in general are terrifying drivers; the Ryder twins are even worse than Shepard, and they presumably learned how to drive from their father, who was one of the first N7s.
• The weaponized omnitools introduced in 3 were, canonically, a revival of a discarded concept due to Reaper forces' emphasis on Zerg Rushing their foes. In fandom, it's a lot more common, appearing as far back as the events of Mass Effect 1, albeit usually in the hands of elite or highly skilled forces, just like in canon. Fanfics also tend to have thermal clips being used as far back as then, in order to fix the Voodoo Shark caused by their introduction.
• Many fans take it as a given that the benign neoplasm that makes it near impossible for Miranda to conceive was intentionally engineered by her father as another means of control. While certainly possible, this is never actually stated anywhere, and it is just as possible that it was unintentional and the very thing that led him to create Oriana.
• There's a surprisingly prevalent belief among fans that the Reapers only produce one Sovereign-class Reaper per cycle. Rather, it is theorized in-universe that the Reapers use a single species to build the Sovereign-class Reapers.
• Another prevalent bit of fanon is that the Citadel is responsible for the strict laws on transhuman technology, especially genetic engineering. In fact, with the exception of a line in the Codex on how medi-gel technically violates Citadel laws on genetic engineering, all restrictions on genetic modification were reactionary human laws in response to perceived threats to the uniqueness of the human genome.
• Officially, Matriarch Aethyta mentions having two children: Liara and another daughter that was fathered by a hanar. Due to the context of the conversation that mentions the hanar and Benezia among Aethyta's past lovers, many fans assume that she has an additional two children; one fathered by a turian and another fathered by an elcor.
• Morinth's place in her siblings' birth order is never stated except that she is older than Falere, but most fans assume that Morinth is the oldest.
• Because Shepard and the party members never become indoctrinated despite being around Reapers and Reaper tech often, some fans interpret it as them being either immune or resistant to its effects.
• While not widespread, there are several fan works that have Quarians still living alongside the Geth on Rannoch, and that the Morning War was not Geth vs Quarian but Pro Rights vs Anti Synth. This troper has read one that had the Migrant Fleet started by said Anti Synth group, most of which were Quarians in the government, the rich, and their families. Meanwhile poor, criminal, orphan, and Pro Rights Quarians remained.
• Rael'Zorah's full name is never stated, but since Tali's full name at the start of the series is Tali'Zorah nar Rayya, it's usually assumed that Rael's is Rael'Zorah vas Rayya.