Coud Van Giruet, known as Cou, spent his earliest years homeless until age five, when the leader of the Red Lynx sky pirates discovered and adopted him. He deeply respects this leader as a father figure, embracing his values of protecting the vulnerable and treating others with kindness. Raised exclusively among male pirates, Cou initially displays naivete and embarrassment around women. His early duties on the ship involved menial tasks due to his notorious lack of piloting talent, a source of frequent comedic mishaps, though he demonstrates gradual improvement. He wields a grappling hook-like weapon named Angel for mobility or basic combat when not fused with an Edel Raid.

During a raid, Cou finds Reverie Metherlence (Ren) sealed within a coffin-like container. After awakening her, he fiercely defends her against Arc Aile agents attempting to purchase her, declaring she is not property. This act earns Ren's trust, prompting her to initiate a "React" fusion to repel attackers. Following the Red Lynx ship's destruction, their leader commands Cou to protect Ren and escort her to her birthplace, Edel Garden. Cou vows to fulfill this promise, embarking on a journey alongside Ren and Arc Aile members Cisqua, Rowen, and Kuea.

Cou's combat abilities evolve significantly throughout this quest. Initially inefficient when fused with Ren, wasting her energy during attacks, he learns better synchronization under Cisqua's guidance. Their fusion enables Ren to transform into a wind-based sword on his right arm, granting access to techniques like Euros Loop (wind projectiles), Notus Chord (energy slashes), Reject Out (defensive barriers), and Zephyrus Art (high-speed strikes). His bond with Ren deepens into mutual romantic feelings, though he struggles to express them. His protective nature extends beyond Ren; he intervenes for other exploited Edel Raids, upholding his belief in their dignity as individuals, not weapons.

Character development defines Cou's arc. Beginning without personal ambitions, his commitment to Ren blossoms into a broader dream: founding his own sky pirate crew, the "Bunny Ears Pirates," composed of allies met during their travels. In the manga's conclusion, he vanishes amid Edel Garden's collapse after Ren is forced to kill her corrupted mentor, Cia. A later message confirms his survival, showing him wielding Ren, which prompts Cisqua's group to search for them. The anime adaptation diverges; he dies battling the Chaos Choir organization but is revived when Edel Garden's queen, Eve, sacrifices her life force. He then reunites with the Red Lynx crew alongside Ren.

In the sequel *Flag of Blue Sky*, set two years later, Cou appears aged 17, continuing his sky pirate activities. His relationship with Ren remains central as they navigate the challenges of a human-Edel Raid bond, including her significantly longer lifespan. His leadership skills and combat prowess show further maturation, reflecting his ongoing growth beyond the original series.