Kirigaya Suguha

is the cousin of Kazuto, she was raised along with him as his sister. She is an accomplished kendo practitioner following in her grandfather's wishes.

She later takes up VRMMORPG playing in «ALfheim Online», as Lyfa (リーファ) a Sylph warrior.

Background
Kirigaya Suguha was raised with Kazuto as his sister when her parent took Kazuto in after his parents died in a traffic accident. Kazuto is Suguha's first cousin; his mother was Suguha's mother's sister. They were taught Kendo by their grandfather, who was a former policeman and a Kendo champion. Kazuto gave up after two years and embraced the world of technology, leaving her behind. The truth is, Kazuto found out he was not her real brother around this time and their distance became further and further apart, until they were practically strangers before the SAO Incident. She continued with Kendo and became a national quarter-finalist. Suguha originally disliked VRMMO's for the reason it hid people's nature and reality. She took up ALO in order to understand Kazuto better when he was trapped in SAO. She won the Sylph tournament earning the title as strongest Sylph before Volume 3. She learned how to play ALO from her classmate, Recon.

Personality
Contrary to her cousin Kazuto, Suguha is more upbeat and outgoing. She is much more social and converses easily with others. Even when Kazuto began to push her away after finding out they weren't really siblings, she still treated him with good spirits and tried to get back in his life. She can be very agressive towards those that annoy her or cross her and can lose her temper making her a little immature, demonstrated when Recon attempted to kiss her after confessing to her she punched him and then beat him up or getting frustrated when Kazuto was dodging most of her attacks in a Kendo spar causing her to hit him over the head with more strength than she intended. Despite treating Recon most of the time with annoyance, she cares for him as a good friend although she does not seem to return his feelings. She did, however, say she enjoyed seeing this side of him when he confessed and was shocked and motivated by his sacrifice in the World Tree.

Despite her positive outlook and slighly aggressive behavior, Suguha can be somewhat fragile and delicate due to her young age espesically when her cousin, Kazuto is involved. Once finding out Kirito and Kazuto were the same person, she locked herself in her room away from her cousin and went into a slight depression. It is also said after seeing Kazuto in a coma being in SAO, she broke down crying for the first time in years. Luckily, most of the time she is quick to rebound from these moments and be the same upbeat girl she always is. She also is the only girl Yui will allow to interact with Kirito, most likely because the two are family.

Sword Art Online
In the anime, she was telling Kirito that she was heading to club activities before Kirito started playing SAO. Throughout the arc, she was mentioned a couple of times.

Fairy Dance
She first is overjoyed to find Kazuto returning home, and tries to be respectful of his temporary weakness. She is also saddened by her brother's new found attachment to Asuna. After a couple months after Kirito's return, Kirito challenges Suguha to a kendo duel. Though she wins she is surprised at Kirito's unorthodox skills. Yet she is also happy that Kirito once again shows interest in kendo.

After logging in on ALO, while flying with her party they are attacked by a Salamander hunting squad. As the battle progresses, she becomes the last survivor fleeing from three pursuers. She encounters a Spriggan after being forced onto the ground, she then helps the Spriggan in it's journey towards Aarun. Suguha later finds out that the Spriggan she had encountered was actually her brother Kazuto.

Caliber SS
She comes to Kirito to inform him that Excaliber's location has been found. They then talk about the new quest that has appeared, where players are requested to kill the beast-type Evil God monsters.