Mattea Farah operates a flower stall in New York, a cover Lupin exploits during an auction infiltration. Their encounters foster a paternal bond, with Lupin frequently purchasing flowers as part of his plans. Yet Mattea conceals a complex reality: she is a sleeper agent within Tomoe's network, a woman trained and manipulated for Tomoe's objectives. Mattea specifically joined this program driven by revenge, seeking to find and eliminate Tomoe for ruining her life.

Injured during a skirmish involving Lupin and Tomoe's agent Mercedes, Mattea recovers in a hospital. She displays fierce resilience there, rejecting Lupin's apology and reframing the trauma as a positive lesson, challenging perceptions of her vulnerability. As Tomoe's influence grows, Mattea becomes ensnared in a confrontation where Tomoe brainwashes Lupin's memories. Under direct control, Mattea is compelled to shoot Lupin, underscoring her role as Tomoe's pawn.

During the climax at the Lupin family mansion, Mattea attempts to assassinate Tomoe, but Lupin shoots Tomoe first. This sparks a violent rooftop struggle between Mattea and Lupin. Even freed from Tomoe's immediate control, Mattea continues her assault, fueled by residual trauma and programming. Inspector Zenigata ultimately arrests her after the fight, though Lupin offers moral guidance before her custody. Her final fate remains open, but her journey traces a path from seemingly innocent flower seller to weaponized agent of vengeance, culminating in a figure grappling with the consequences of her conditioning.