Game of Thrones has been accused of many things over the years (excessive nudity! Gratuitous violence!), but never this. As the HBO show drew the curtain on its latest episode, The Long Night, fans of the show berated the showrunners, David Benioff and DB Weiss, for committing a cardinal sin of scriptwriting: the “Mary Sue”.

In fanfiction parlance, a Mary Sue is a female character so faultless that she strains credulity. As Vox put it: “Every subsection of fanfiction has its own priorities and grievances, but the derision toward so-called Mary Sue characters is nearly universal.”

The term was coined in 1973 by a Star Trek fan, Paula Smith, who named a flawless parody character Mary Sue in a story for the fanzine she edited. She was tired of seeing so many young women who were too unrealistic to be interesting.

For those who have yet to squint through the episode’s 82 minutes of badly lit flying body parts and dragon fire, the teenage assassin Arya Stark (Maisie Williams) has been criticised after pulling off an audacious last-minute manoeuvre that turned the tide in favour of the living during the climactic battle against an army of zombies.

“Mary Sue Stark to the rescue! Really?” wrote one Reddit user. “Its [sic] just a bunch of Disney/Marvel/etc feminist Mary Sue horseshit,” opined another. At one point, the phrase began trending on Twitter, although it appeared to be fuelled by people outraged by the idea Arya could be considered a Mary Sue.

Even Williams was nervous about the episode. “I immediately thought that everybody would hate it, that Arya doesn’t deserve it,” she told Entertainment Weekly.

However, eagle-eyed viewers of the show will note that Arya’s torturous journey from orphaned stray to ultimate zombie-killer has been in the works since she picked up a wooden sword under her first tutor, Syrio Forel, in season one. Is Arya a Mary Sue? Not if you take into consideration a meticulously plotted, eight-season-long character arc that turned her into the ultimate killing machine and left her with emotional baggage to rival Breaking Bad’s Walter White.

In any case, the show excels at twists. Say what you like about Game of Thrones, but it still manages to surprise, 70 episodes in.