Hanako was born in the Year of the Dragon. She had a blissful early life until she turned 5. Her parents died in the Las Vegas Shooting on October 1, 2017. Heartbroken, she was taken to the social services and adopted by the Kirigaya family. Little did she know, her best friend lived under the same roof as her.
When the Sword Art Online Closed Beta was announced, Hanako immediately signed up. She logged hundreds of hours of gameplay and was one of the top players. She pre-ordered the game and when it came, she locked herself in her room before logging in to SAO. Soon, the death game began.
As a young woman who is barely blossoming, Hanako has a fragile personality. She has an uncontrollable lust for her "big sister", Shioko, after discovering that she also is playing SAO. Unfortunately, she has competition. Her sister already has a group of people who are trying to win her affection. Hanako's biggest problem is Yuurei, the Flash. Other than her, there is Tiffany, Chelsea, Asano and, Quartz. Hanako figures she could shrug off everyone except for Yuurei. Her love is now again interrupted by a new figure, Rain. On Floor 53, Shioko and Rain exchange vows of sisterhood while Hanako looks on in jealousy.
By the end of Dreamscape, Hanako had lost in the battle to win her sister's love. Shioko was head-over-heels with Yuurei. On the bright side, Hanako and Quartz end up together. Quartz is two years older but treats Hanako with dainty respect. On Floor 98, they share their first kiss, in full view of her sister. Shioko gives Hanako a kiss on the forehead and promises to protect their relationship. Even if they aren't real siblings, Hanako and Shioko share an extremely deep connection.
During SAO, Hanako, known as Illyasviel or just Illya, has equipment that could be considered not safe since it did show off more skin than she had intended to. It didn't matter to her since it was necessary to make some sacrifices during battle. Her main weapon during the Chaos Labyrinth arc was called «Pierce», a crimson spear. In the third volume, Hanako had discovered her Dual Spears unique skill. Since she did not know the prerequisites, she kept it secret until it was necessary during the boss battle on Floor 48. Her second main weapon was a gold spear, «Round Table Lance».
In ALO, her equipment does cover her skin which was a relief to her friends but it was still a bit over the top. The fabric making up the vestment was completely see-through so people could make out her undergarments. Shioko informed her that her Dual Blades skill was still usable to which Hanako excitedly began logging more hours. Her first spear was the «Aslegeion Avatar» which she had saved into her NerveGear for transfer into ALO. Three months later, she obtained the «Gáe Bolg» and sold her Aslegeion Avatar.