Fou Lafine spent his childhood orphaned in the war-ravaged city of Sodom after a bombing claimed his parents' lives. This forged him into a self-reliant, aloof teenager, maintaining closeness only with Lily and her brother Quattro. From a young age, he displayed exceptional musical talent, mastering the violin, organ, and harmonica, playing primarily in churches for sustenance rather than faith. He cultivated a deep aversion to religion, seeing it as passive and powerless against the war destroying his home.

After Lily's death, Fou and Quattro were recruited by soldiers of the Machine Empire. Unaware the Empire itself orchestrated Sodom's destruction, Fou underwent rigorous training alongside fellow orphans Ron and Karen, initially believing in the Emperor's mission for "true peace." His combat prowess and strategic brilliance earned him the rank of major and a place among the Empire's four legendary Spirit Generals, becoming the donor to the phoenix-type B't, Je t'aime.

Fou's loyalty later became suspect when he deliberately allowed Karen to defect, resulting in his demotion to lieutenant. Despite his military role, he simultaneously operated a church offering refuge and care for orphans, revealing a compassionate side starkly contrasting his soldier's duties and highlighting his complex relationship with the Empire's ideals.

During the events of the sequel, Fou confronted his past through a bitter conflict with Quattro, who resented Fou's harsh dismissal of religion at Lily's deathbed. This forced Fou to reconcile with his actions; he initially considered letting Quattro kill him as atonement but moved beyond this impulse. He focused instead on protecting the orphans under his care and aligning more decisively with the protagonists against the Empire.

Fou's combat abilities centered on his signature weapon, the Funeral Bow, which doubled as a violin bow capable of unleashing lethal arcs of high-voltage electricity. His "Fortune Symphonic" technique amplified Je t'aime's powers through specific violin melodies, forging psychological and emotional connections with listeners. These skills, combined with tactical intellect and agility, made him a formidable combatant.

Throughout his journey, Fou wore a pendant given by Lily—a cross in the manga, a triangle in the anime—symbolizing his enduring connection to his past. His character evolved from a disillusioned orphan and loyal soldier to a protector of the vulnerable, driven by a desire to rectify the Empire's injustices while honoring those he lost.