Overview

Kirito and Asuna are players trapped within Sword Art Online - a deadly VRMMORPG game in which players die in real life once their HP reaches 0. They fight at the front lines of Aincrad, a floating steel castle made up of 100 floors, aiming towards the clearance of the game in hopes of getting back to the real world. Kirito is a solo swordsman, while Asuna is a fencer and subleader to the guild "Knights of Blood". They are sworn life-and-death partners, having fallen in love with each other after experiencing many perilous situations together. They get married in-game and later on adopted Yui, an AI daughter.

Their relationship still goes strong in real life after SAO is cleared, despite many different worlds they are in and extreme obstacles that split them apart.

SAO

As players fighting at the front lines, Asuna usually asks to hang out with Kirito and later even forms a party with him. Kirito, with low self-esteem, would shyly accept her offers, although he does have a crush on her. After a certain dangerous incident, Kirito proposes to Asuna, and they move in a log house on Floor 22 to live their honeymoon life. They meet an AI named Yui there and consider her their daughter, even after escaping SAO. Around the end of SAO, Kirito and Asuna both express their passionate love to each other, and the will to live and support solely for one another, for the rest of their life.

SAO Progressive

Kirito and Asuna, but at the beginning stages of clearing SAO, when they are still middle-schoolers aged 14-15. They first meet inside a dungeon of floor 1, form a 2-people party and take part in the floor's boss raid. After a short split-up, the regroup on Floor 2 and continue to travel and fight alongside one another. They would pull jokes upon each other (Asuna would often punch Kirito as paybacks), share meals, sightsee together and even sleep on the same bed. Kirito is very protective of Asuna, and Asuna is very supportive of him, often using physical touch to show her support. Although both hold mutual, powerful feelings for one another and wishes to be beside each other, Kirito does not think he deserves to be with her, as he considers Asuna someone who would shine at her utmost potential without him; while Asuna, despite actually really enjoys being with Kirito, does not openly shows affection for him because of her still dishonestly acting cold to him. Their partnership ends after Floor 25's boss is defeated.