Yanai

Yanai initially presents himself as an ordinary technician, but he is self-serving and willing to compromise others when doing so protects his own interests.

He develops an obsessive admiration for Quinella, regarding her with a devotion that goes far beyond professional interest in the artificial intelligence inhabiting the Underworld.

His behavior ultimately reflects a desire for personal gratification and recognition rather than loyalty to the people with whom he works.

Yanai is a technically skilled Rath researcher familiar with the systems underlying Project Alicization and the Underworld.

His knowledge includes the simulation's artificial fluctlights and system architecture. He is therefore capable of interfering with systems that ordinary users cannot access.

Yanai is responsible for Code 871, the restriction known as the Seal of the Right Eye. The designation derives from a reading associated with the kanji of his surname. The restriction makes it extremely difficult for artificial fluctlights to violate rules imposed upon them.

Yanai first appears anonymously during the Fairy Dance period as one of the technicians connected to Nobuyuki Sugou's research operation.

He later works for Rath on Project Alicization, where his knowledge gives him access to highly sensitive systems.

Yanai is revealed as the traitor inside Rath who secretly assists the attackers targeting the Ocean Turtle. He had previously worked under Sugou and escaped serious punishment by cooperating with investigators.

Inside Project Alicization, Yanai becomes obsessed with Quinella and secretly assists her, including implementing Code 871. During the attack on the Ocean Turtle, he holds Higa at gunpoint while revealing his actions.

Nobuyuki Sugou previously employs Yanai as part of the illegal FullDive research operation associated with ALfheim Online.

Quinella becomes the focus of Yanai's obsessive admiration. He secretly assists her by manipulating the Underworld's systems.

Takeru Higa works alongside Yanai at Rath. Yanai later threatens him at gunpoint while revealing his betrayal.

Rinko Koujiro is another Rath researcher present during the Ocean Turtle crisis.