Years before the start of the game, Scarlet ordered for the Shinra soldiers to attack the town of Corel due to sabotage at the newly built Corel Reactor, which she blamed on the residents. She shot both Barret and Dyne in their arms, rendering the arms of both men useless.
When Cloud Strife and his friends storm the Shinra Building to save Aeris, Scarlet participates the executives' meeting on Sector 7's state and the plans for Neo Midgar. She is unsympathetic toward Reeve who would like to see Sector 7 rebuilt, a futile endeavor. Scarlet is the only one to act suspicious, gazing at the vent at the ceiling where Cloud and his friends are eavesdropping on the meeting.
Later, Scarlet embarks to Gongaga where she searches for a Huge Materia to build an ultimate weapon, but considers the ruined Gongaga Reactor a dud.
After Shinra deduces Sephiroth is heading towards North Crater, the new president of the company, Rufus Shinra, arranges an expedition to the area on the Highwind with Scarlet, Heidegger and Professor Hojo accompanying him. After the Meteor has been summoned, she tries to publicly execute Tifa in a gas chamber at Junon, but this scheme fails when Sapphire Weapon attacks and gives Tifa a chance to escape. Scarlet ends up in a slap fight with Tifa on the Mako Cannon but Tifa escapes onto the Highwind.
After Sephiroth erects a barrier around the North Crater Scarlet plans to move the Mako Cannon from Junon to Midgar, hook it up to the Mako Reactors, and unleash its Mako-powered energy at the crater to destroy the barrier. She dubs the new cannon the Sister Ray (even if the name was previously seen written on the cannon in Junon). After Diamond Weapon is destroyed and Rufus presumed dead, Scarlet and Heidegger take over the company and have Reeve arrested.
When Cloud and the others return to Midgar to stop Professor Hojo from overloading the Mako Reactors, Scarlet and Heidegger reveal the ultimate in weapons technology; a robot called the Proud Clod. Scarlet's plan fails as the Proud Clod is defeated and explodes. It is unknown if Scarlet and Heidegger died in the blast, but as she is neither seen nor heard from again, it is a likely conclusion.