WARNING: the following contains spoilers for Sword Art Online Progressive: Aria of a Starless Night, now playing in theaters.
As part of Sword Art Online Progressive: Aria of a Starless Night's goal of reimagining the "Aincrad Arc," the movie makes Asuna its protagonist. In doing so it not only changes the overarching story but also gives fans greater insight into the Lightning Flash as a character. By focusing on Asuna, the movie shows an interesting side of her that fans might not think about or even realize exists.
Apparently, when Asuna first logs into SAO, she does so as a total novice. There are hints of this in the original anime, but the movie makes it clear that she's starting off with no idea what she's doing. This runs in sharp contrast to Kirito, who enters SAO as a beta tester as well as a veteran gamer. It's also surprising to see her like this as she's shown throughout the anime as a skilled and competent player. Asuna's amateur gamer status not only paints the Lightning Flash in a new light but also drives the plot of the "Aincrad Arc" in a new direction.
Asuna's inability to play video games is the result of her upbringing. Normally Asuna's family wouldn't appear until after Aincrad, but with the movie being told from her point of view, it's an opportunity to expand upon this aspect of her life. It's established that since her mom is what the Japanese call a kyōiku mama (education mother), the girl must prioritize studying and schoolwork over all other interests. Asuna's focus on academics not only explains her lack of video game skills but also contextualizes her thoughts, decisions, and actions throughout the movie. There's even a scene later in the movie where she equates falling behind other players to dropping out of the top 10 in one's grade.
The only reason Asuna has even a passing interest in SAO, or video games in general, is that her friend Misumi invites her to play. Unlike Asuna, Misumi is a professional-level gamer who attracts crowds around her when she plays at the local arcade. Asuna will play against her occasionally, but never with the expectation that she'll win. Asuna has no drive to get better at video games and, for how she lives her life, she doesn't need to. She gives SAO a try because her friend is there, and not much else.
Even with Misumi's invitation, Asuna's entry into SAO is entirely circumstantial. She happens upon a NerveGear and a copy of the game in her brother's room while he's away on business. If all these coincidences hadn't lined up so perfectly, Asuna would never have been trapped in the game with everyone else.
When she first signs in and arrives at the Town of Beginnings, she does a number of things that only a newbie would do when playing games. She uses her real name for her profile, uses an avatar that looks like her, and talks to NPCs like they're actual people. She even gets called out for all this by the other players, including Misumi (username: Mito). These aren't necessarily bad things, and one of them becomes a moot point anyway, but they are tell-tale signs of somebody unfamiliar with gaming culture.
Asuna's inexperience comes back to bite her in a scene the movie shares with the anime. At the end of the first episode when Kirito leaves the Town of Beginnings, he is attacked by a Dire Wolf but manages to make quick work of it. This scene is mirrored by Mito in Aria of a Starless Night. As for Asuna, the Dire Wolf goes straight for her throat and almost whittles her hit points down to nothing. This scene is intense in the context of the movie, but it's also hilarious when juxtaposed with the anime.
Rather than shake off the Dire wolf or fight back, Asuna freezes in fear and despairs her imminent death. It's only when Mito defeats the Dire Wolf for her that she is saved. Asuna's response to this situation highlights how out of her depth she is as well as the true peril of SAO.
Storywise, a greenhorn main character lets viewers see more of what it's like to learn to play Sword Art Online. When Kirito was the lead, this gameplay aspect wasn't be properly explored because he's already an expert at the game. The only glimpse viewers see of what things are like for amateurs is when he's teaching Klein at the start of the first episode. From then on, most of the other players are shown to be at least fairly capable in their own right. Aria of a Starless Night uses Asuna to show more of what it's like to just be learning the ropes.
Asuna's training makes for some surprisingly entertaining material. It's easy to assume that the only way to keep a story engaging would be with increasingly dangerous threats. However, if that were the case, there could never be reboots in the first place. Watching Asuna struggle with the basics before she finally overcomes her first enemy on her own is both exciting and satisfying. Asuna's improvement lets viewers breathe a sigh of relief when they see that their main character won't immediately die to whatever she's put up against. It also provides a bonding experience with her instructor and friend Mito.
Sadly, Asuna's overall lack of still is still a detriment to her. She has trouble dealing with multiple enemies and nearly dies to a stronger-than-average op0ponent. In the latter situation, she still has to be saved from certain death by another player, namely Kirito. Asuna's near-death experience combined with the news that nobody has even cleared the 1st Floor yet puts her in a deep depression.
Asuna decides to do the one thing any RPG player can do to ensure her survival-- grinding levels. Most RPGs set their enemies and bosses at a level they expect will give the player difficulty. At a high enough level, however, most threats cease to be challenging. She spends days in a dungeon fighting weak monsters and steadily earning experience points. She also decides not to bring healing items because she's confident that she can avoid taking damage, something that players of any game should strive for. This is a slow method for improvement, but it apparently works for her.
The fruits of Asuna's labor come to light during the raid against the 1st Floor Boss Illfang the Kobold Lord. She radiates confidence, coordinates well with her teammates, and even advises them on their best course of action. In terms of battle prowess, she is good at landing fast strikes while avoiding damage. In the anime, this would be the point where Kirito isn't sure whether or not she's actually a novice. Kirito's perplexity isn't in the movie, but there is a line about how he and Asuna are two of the top players in the game after they beat Illfang. Seeing Asuna finally look like a pro gamer is awesome, especially in the context of all her ordeals.
Of course, Asuna's lack of gaming knowledge does eventually shine through. During the fight, Kirito calls her by her name, but this confuses her because she never told it to him. When she asks about it, Kirito explains that she can see her party members' names and health bars under her own on the HUD. She finds this oversight on her part amusing and laughs it off. It's minor, but it is funny to see how so much can change yet stay the same.
Aria of a Starless Night may start Asuna off as an absolute noob, but that's part of the fun. Seeing the fledgling Lightning Flash slowly work her way up to earning that title is an engaging experience. It's also one that couldn't be covered in the anime since most characters presented in that series are already seasoned gamers. Watching Asuna persevere through hardship and become one of the top players in SAO is both inspiring and entertaining.