Rinko Koujiro is a scientist who studied at Toto Institute of Technology in the Electrical and Electronic Engineering Department's Shigemura Lab. She met Kayaba Akihiko, her former love interest and co-worker, during her first year of college. Rinko assisted in developing Sword Art Online but remained unaware of Kayaba's plans for the game.

During the SAO incident, Rinko deduced Kayaba's location and traveled to his mountain cottage intending to stop him. Unable to harm him, she instead cared for his physical needs during his extended dives. After Kayaba's death, authorities arrested Rinko, but she was later acquitted due to fabricated evidence Kayaba planted—a fake micro bomb implant suggesting she was coerced. Following her release, she moved to California to develop the medical FullDive device, the Medicuboid, based on Kayaba's research data.

In 2026, Rinko received an email from Asuna Yuuki concerning Kazuto Kirigaya's disappearance and involvement with Kikuoka Seijirou. She agreed to help and traveled with Asuna, disguised as her assistant, to the offshore facility Ocean Turtle, run by Rath. There, she learned about Project Alicization, which aimed to create artificial Fluctlights for military applications using Soul Translator technology. Rinko assisted Asuna in understanding Kazuto's condition and the project's scope.

During the Ocean Turtle crisis, Rinko intervened to save Higa Takeru from an attack by the traitor Yanai, enabling Higa to focus on restoring Kazuto's damaged Fluctlight. After the conflict, she assumed leadership of Rath following Kikuoka's departure. In this role, Rinko oversaw technical adjustments for Alice Zuberg's artificial body as Alice transitioned to the real world. She also discreetly supported Alice's stay with Kazuto's family, facilitating her adaptation to human society. Her actions are dedicated to realizing Kayaba's underlying goal of creating genuinely adaptive artificial intelligences beyond military use.