Keiko Ayano, known in virtual reality games by her player name Silica, is a supporting character who appears in the Sword Art Online: Extra Edition film. Her real name is Keiko Ayano, and she is a young Japanese girl born on October 4, 2010. During the events of the original Sword Art Online death game, she was only twelve years old, placing her among the youngest players trapped inside the game.

In the virtual world, Keiko is known for her bright, cheerful, and kind personality, always showing strong support for her friends. She has a deep attachment to her familiar, a feathered little dragon named Pina, whom she tamed in SAO. This bond is so profound that the thought of losing Pina is heartbreaking to her. Although she is generally friendly and loyal, she was once prone to a degree of arrogance due to her fame as a rare beast tamer in the game. This overconfidence led to her becoming separated from her party in the Forest of Wandering, which resulted in a critical incident where Pina sacrificed its life to save her from a monster attack. This event served as a significant lesson, curbing her recklessness and contributing to her growth as a person. She is also easily flustered or embarrassed, especially in situations involving romance or when witnessing public displays of affection between other couples. A running source of insecurity for her in the real world is her youthful, petite physique, particularly when compared to some of her friends.

In Sword Art Online: Extra Edition, Keiko plays a key role by participating in a swimming tutorial organized for Kirito's cousin, Suguha Kirigaya, who is trying to overcome her fear of water in the real world. Alongside her close friend Rika Shinozaki, known as Lisbeth, and Asuna Yuuki, Keiko helps teach Suguha how to swim in a school pool. During this time, the group reflects on their past experiences in Aincrad, with Keiko talking about her first meeting with Kirito and the harrowing adventure they shared to revive Pina. Later in the Extra Edition story, the group logs into the game ALfheim Online to undertake a new quest called Deep Sea Plunderers. Within this virtual world, Keiko's avatar is a member of the Cait Sith or cat妖精 race, which grants her feline features such as cat ears and a tail. She continues to use a short dagger as her primary weapon and is accompanied by her faithful dragon, Pina, who was successfully transferred to the new game.

Throughout the wider series, Keiko's key relationships are central to her character. Her bond with Kirito is particularly significant; she initially held romantic feelings for him after he helped her, but she eventually came to view him as a big brother figure, especially after he mentioned she reminded him of his own sister. She also shares a strong friendship with Lisbeth, and the two girls formed a humorous pact to watch over Kirito and Asuna's relationship from a respectful distance. In terms of abilities, Keiko is recognized as a beast tamer, a rare and notable skill in SAO that allowed her to befriend and control a monster companion. In combat, she wields a one-handed short dagger, employing sword skills such as the medium-level thrusting attack "急咬" and the consecutive strike skill "短刃". Her familiar Pina also provides support in battles, possessing abilities like Healing Breath, which restores a portion of Keiko's hit points, and Bubble Breath, a non-damaging magical attack with confounding properties that can hinder enemy movements. While her role in Extra Edition is focused more on character interaction and a lighthearted quest, her established background as a resilient survivor of the SAO death game underpins her actions, demonstrating her transition from an impulsive beginner into a more mature and reliable ally.