Sword Art Online is an action adventure anime with a lot of romance; especially since it is about a game where the players discover they are trapped in a Death Game with one simple objective: to clear the 100 floors and beat the game. The catch was just as simple: if a player died in-game, then they died in real life.
Former beta-tester Kirito (a.k.a Kazuto Kigiri) is a solo player and the main character of the anime. He falls in love with Asuna (a.k.a. Asuna Yuuki), another player who is also the second-in-command to the Knights of the Blood Oath guild. The romance between Kirito and Asuna starts off in a tentative friendship that later deepens to a love that determines the fate of two different virtual reality games, as well as the fate of thousands of players.
The romance between Kirito and Asuna takes almost two years to develop in the SAO arc. They meet for the first time while joining in on a strategy meeting to defeat the first floor boss within the first month of the game. Since they are both solo players, Kirito convinces Asuna to party with him for just the one battle and Asuna hesitantly agrees.
Asuna is still cautious of her teammate, however, and prefers to keep her distance from Kirito. Kirito tries to make some effort to get to know her anyway, and eventually Asuna responds by sharing her fears. She's afraid of rotting away in-game and forgetting who she is if she remains in the Town of Beginnings. Kirito can only respond by saying that he hopes he doesn’t lose a party member in battle.
During the battle, they work well together. Kirito’s fear of losing Asuna is diminished when Asuna fights. Her skills are good for a beginner. Asuna is quick, graceful, and competent with her rapier. He’s impressed. When her protective cloak is destroyed, Kirito is momentarily stunned by Asuna’s true appearance.
When Kirito goes to leave at the end of the battle, he leaves Asuna with the advice to join a guild with someone she trusts so she can get stronger as a player.
Asuna takes his advice and joins the Knights of the Blood Oath and earns the second-in-command position within a few months. Kirito is astonished by her quick rise in the game, but now they clash with a difference of opinions during strategy meetings.
Roles are also slightly reversed: Kirito is no longer eager to make a ton of friends while Asuna is well-respected as a player and leader.
Kirito is taking a nap in the shade of a tree when Asuna finds him. She lectures him on how everyone on the assault team is working to clear the game and he should be working alongside them. Kirito seems indifferent with her scolding and comments that the day’s weather is at its optimal setting.
The difference in their philosophies plays an important part of the beginning of the romance. His comment sets Asuna off even more, and she tells him that every day they spend in-game is another day wasted in the real world. Kirito tells her that he’s alive and in Aincrad at the moment and he’s going to enjoy the day. Asuna is surprised and begins to consider his words while studying the surrounding area. The countryside was indeed beautiful. Until Kirito, Asuna’s sole goal in life is to clear the game and resume her former life. Now she begins to reconsider her motives.
She feels comfortable around Kirito and decides to try living, just for a moment, like him and falls asleep in the shade of the tree. Kirito sits up and is shocked to discover Asuna sleeping. He watches over her until she wakes so she won’t get killed by player-killers. Asuna is flustered and embarrassed when she wakes and finds Kirito watching over her. Her sense of honor dictates that she should repay him somehow and offers to buy him dinner.
Circumstances force them to work together to solve a murderous situation and they discover they still work well together. Asuna opens up more to Kirito and he learns that even though Asuna is eager to beat the game, she still finds little things like in-game marriage romantic---in a practical way of course.
By the end of the dispute, they have a better understanding with each other and part as friends. Over the course of the Sword Art Online arc, Kirito and Asuna continue to run into each other and work on their friendship over the next two years.
Asuna is generally the first to make an overture of friendship because Kirito tries to keep his distance from other players. Several times, Asuna is called out about her feelings towards Kirito, but she is quick to deny that she has any romantic feelings towards him. Kirito, meanwhile, is usually pleased to see her and is quick to help her if she needs it.
Kirito catches a rare S-class food item called a Ragout Rabbit Meat. Disappointed his cooking skills aren’t very high, he decides he has to sell it to his friend Agil and miss the opportunity to eat the delicious meat. Asuna surprises him by showing up in the shop at the very moment looking for him “to check that he’s still alive” though she could have easily checked her Friend List.
Her cooking skills are maxed out though and she agrees to cook the rabbit in exchange for half of the meal. Her excitement for cooking the exotic meat causes Kirito to look at her fondly, and they head to Asuna’s house for dinner.
Kirito sees Asuna dressed in casual clothes for the first time and shocked by the transformation from second-in-command to a normal girl. He is equally impressed with her cooking. The night seems to be almost normal (as far as life in-game goes at least) and Kirito is somewhat uncomfortable with the domesticated Asuna. She picks up on his discomfort and warns Kirito against proposing to her, much to his embarrassment. Kirito’s retort is that he’s a solo player which leads to a discussion about guilds and joining other players.
In the end, Asuna decides she’s going to join Kirito in a party. He tries to dissuade her, unsuccessfully.
While teamed up, they fight a boss where Kirito comes dangerously close to losing his life. Asuna rushes over to him after he collapses. The reality that she almost watched Kirito die encourages her to announce that she is taking a leave of absence from the Knights of the Blood Oath so she can team up with Kirito indefinitely.
Her plans don’t go exactly her way, however, when Heathcliff, the Commander of the Knights of the Blood Oath, refuses to let her leave. He suggests a deal instead. He wants to duel with Kirito. If Kirito loses, Kirito must join the Knights. Kirito agrees, confident in his abilities. Unfortunately, Kirito’s skills are no match for Heathcliff and he loses.
Asuna feels bad about Kirito being forced to join the guild when he wanted to remain a solo player. He manages to convince her that it was time for him to stop being a solo player anyway.
Life in the guild is not easy for Kirito. Asuna later rushes to his rescue when a player-killer tries to kill Kirito. They end up rescuing each other and this time, it’s evident that they are, in fact, in love with each other.
Crisis adverted, Asuna and Kirito admit their feelings for each other and they decide they want to get married in-game. Pooling their money together, they buy a quaint house in the woods and take a little honeymoon. For the first time in two years, Kirito and Asuna feel a sense of belonging with each other while living in their house in the woods.
The deep love they feel for each other is a major factor in clearing the game. Kirito wakes up in his hospital bed and struggles down the hall to find Asuna so they can meet in real life.
The ALfeim arc is different than the Sword Art Online arc. This time, Kirito is on a quest to find and rescue Asuna. Two months have passed after clearing Sword Art Online. Kirito is still gaining strength from his long coma. He regularly visits the hospital where Asuna remains attached to the NerveGear, asleep, for unknown reasons.
After a disturbing confrontation with Asuna’s “fiance”, Sugou Nobuyuki, Kirito goes home, desperate to find a way to help her but unable to do so. His feeling of helplessness is apparent when he breaks down crying in his room.
He receives an email from Agil with a photo attachment. The picture shows a blurry girl locked in a cage who looks suspiciously like Asuna. The picture is from a new VRMMORPG called ALfheim Online and Kirito borrows Agil’s copy of the game to investigate.
He has a one-track mind when it comes to finding Asuna, and he jumps immediately into the game. He discovers Asuna is being kept at the World Tree, the so-called final objective of the game based on the game's mythology. In other words, in order for him to rescue Asuna, Kirito must beat the game. And quickly, before Sugou is allowed to marry a comatose Asuna. His first rescue attempt is flying straight up to the top of the tree but fails due to the game mechanics.
He keeps trying different ways to get to the top of the tree, failing over and over when trying to reach her, but he has regained his hope and purpose. His failures spur him to greater feats to find the woman he loves, leading to a final confrontation at the World Tree with Sugou, the game master.
Meanwhile, Asuna is fending off the lecherous advances of Sugou who is determined to have her at whatever the cost. She works hard to find a way to escape and return to Kirito, not knowing until the very end that he is also in-game looking for a way to save her.
Asuna in Sword Art Online was powerful and able to take care of herself. In ALfheim, she’s trapped in a cage unable to do anything to save herself and is forced to wait. Her situation, compounded with the fact that she is desperate to see Kirito, leads her to a helplessness similar to what Kirito feels at the very beginning of the ALfheim arc before he receives the email with her blurry picture. Both characters fail over and again, but their love for each other motivates the characters to keep trying to reach their goals.
Kirito does find Asuna and he, once again, changes the fate of ALfheim Online by battling the main villain. The world of virtual reality games behind them, Kirito and Asuna are finally able to meet offline for the first time.