Born Karl La Hire, crown prince of the Balsteros Empire, Kal-el Albus spent his early childhood in Alexandra with limited parental contact, though maintaining closeness with his mother during their infrequent interactions. The Wind Revolution abruptly shattered his royal life. Dissidents, led by wind-controlling priestess Nina Viento and Frontier Duke Ameriano, overthrew the empire in a single day. Karl witnessed his father's execution and was imprisoned with his mother, facing her imminent death. Observing an aircraft in flight, he envisioned escape and resolved to become a pilot. His mother's final plea urged forgiveness over hatred, yet her execution cemented his vow of vengeance against Nina Viento.

Slated for execution, Karl was spared when mechanic Michael Albus adopted him. Renamed Kal-el Albus, he joined Michael's family, including daughters Ariel, Manuelle, and Noelle. Despite being only one day older than Ariel (born June 6 to her June 7), their contentious sibling relationship featured persistent arguments over seniority and maturity. Kal-el grappled with timidity and grief, often crying secretly at night. His royal identity was revealed to Ariel when she witnessed him defending an actress portraying his mother in a revolutionary reenactment. Michael Albus reignited Kal-el's passion for flight during a test flight, urging him to discover the "End of the Sky."

Enrolling in Cadoques High's aerial division on the floating island Isla, Kal-el trained as a pilot alongside Ariel. His life shifted upon meeting Claire Cruz, a noble girl posing as a student. After fixing her bicycle, mutual romantic feelings blossomed during flight training, where they became partners. Their bond deepened through shared survival, culminating in a kiss after their first combat engagement against the Sky Clan. This moment coincided with Kal-el discovering Claire's true identity as Nina Viento, the architect of his family's downfall. The revelation devastated him, triggering withdrawal and internal conflict between love and hatred.

Combat against the Sky Clan intensified his struggles. Ariel sustained permanent injuries battling the Sky Clan ace "Silver Fox," ending her pilot career and prompting her transition to mechanic. Witnessing the deaths of comrades Mitsuo Fukuhara and Wolfgang Baumann compounded Kal-el's trauma. His half-brother Ignacio Axis, harboring resentment towards the royal family, confronted Kal-el's despair, compelling his return to battle. Defending the Luna Barco warship, Claire (as Nina) apologized for killing his mother and reaffirmed her love. Recalling his mother's teachings, Kal-el forgave her, shouting "Claire! Live!" as the ship fell. This act restored Claire's wind powers and saved the vessel. Accepting her necessary departure with the Sky Clan to ensure Isla's safety, he vowed reunion, taking her necklace as a keepsake.

After Isla's return, Kal-el addressed the Balsteros public in a balcony speech. He renounced vengeance, emphasizing forgiveness and love while announcing a mission to rescue Claire. Admiral Luis provided the advanced "Maestra" prototype fighter, boasting enhanced speed and weaponry. Leading the Balsteros-Levamme coalition forces against the Sky Clan in this aircraft, he later appeared in the broader conflict of "Toaru Hikuushi e no Seiyaku." As part of the Second Isla Fleet, he participated in pivotal battles across the archipelago region. After six and a half years of separation, he successfully reunited with Claire during the campaign's climax.

Ariel's unrequited romantic feelings surfaced as Kal-el departed for this mission, her acknowledging "some love songs aren't meant to be sung." His character arc concluded with his return to Akitsu alongside Ilya and Kiyoaki, symbolizing the transition from vengeance-driven royalty to a pilot dedicated to protection and reconciliation.