Sword Art Online Season 1 Episode 21

The Truth about Alfheim

Kirito and Leafa reach Arun, the capital of Alfheim, located directly beneath the world tree. However a sudden announcement of an emergency shutdown for server maintenance prompt the two to find a nearby inn and log out. The next day, Suguha accompanies Kirito to visit Asuna at the hospital. Meanwhile, in the World Tree, Asuna stumbles upon a room where experiments are being made with the brains of the other SAO players trapped in ALO. She then attempts to log out of the game by using the GM console inside the room, but is captured by two of Sugou's assistants. However, she manages to snatch a key card before being thrown back to her cell. Back in the real world, Suguha gets heartbroken upon seeing Kazuto tending to Asuna, and is comforted by Kirito after she logs back as Leafa on ALO, still unaware that both him and her brother are the same person. Later as the pair approach the World Tree, Yui suddenly detects Asuna's presence, prompting Kirito to fly ahead leaving Leafa behind.