Serenoa aligns with Legato and Floro, stationed beside a rocket as Maris Excelsior arrives alongside Soushi Minashiro and two Esperanto children. She guides the group to a secured site, aiding in its defense during confrontations. Her striking physical similarity to Yumiko Hino sparks recognition from Maya Toomi, who identifies the likeness to her sister during their encounter.

In combat, Serenoa initiates mental incursions against pilots such as Rina Nishio, seeking to absorb their consciousness and commandeer their Fafners. These attempts falter under external disruptions—notably Kenji Kondou’s interference—prompting Rina to activate the Fenrir program. The ensuing backlash destroys Serenoa’s Fafner, startling her with Rina’s resolve to annihilate herself rather than submit.

She orchestrates tactical maneuvers, mobilizing Festum swarms to neutralize threats like Misao Kurusu’s forces. Amid crises—Floro’s vanishing and their island’s disintegration—she coordinates with allies such as Maris and Legato. Her persuasive tactics surface when courting Kouyou Kasugai and Misao, proposing integration under Marespero’s dominion, though both rebuff her offer.

During assaults on Wadatsumijima and Alvis’ L-Boat, Serenoa deploys psychological warfare, mimicking Miwa Hino’s late mother to breach her psyche. Soushi’s intervention foils the ploy. In combat, she adapts swiftly, teleporting to evade lethal strikes from advanced Fafners like Mark Nicht and Mark Alles. These encounters provoke her first tremors of fear, confronting the potential erasure of her existence.

Persistently, Serenoa prioritizes her faction’s objectives, retreating strategically when overwhelmed. Her drive stems from a conviction to reunite with Soushi and fulfill Marespero’s ambitions—convictions tested by mounting opposition and flickers of doubt.