Princess Rosa Cossette D'Elise, usually referred to as Cossette or Princess Cossette, is a member of the Kingdom of Erusea's royal family. She is the daughter of the man who became King of Erusea for around seven years[note 2] prior to the Lighthouse War. She appears as a minor character in Ace Combat 7: Skies Unknown.
The militaristic, radical factions within the Erusean armed forces convinced Cossette that the International Space Elevator was a violation of Erusea's sovereignty. They further convinced her that Osea sought to rule the Usean continent and that Vincent Harling himself wanted to destroy the space elevator. After discovering she was misled, Cossette joined Avril Mead in sabotaging the space elevator and ending the war. 
Cossette was born into a family of commoners in circa 2001,[note 1] when Erusea was officially a federal republic. The Independent State Allied Forces declared victory in the Continental War in 2005, and Erusea's provisional government reinstated the monarchy three years later. Cossette's father's cousin suddenly became the King of the new Kingdom of Erusea, ascending her and her family to royalty status. Cossette's father tailored suits for both him and his brother when the latter became King after the former fell ill and passed away. 
The general public looked down upon the royal family for some time since they were formerly mere commoners. The young Cossette's parents continued to send her to primary school under a pseudonym, Rosa Cossette Falcinelli. She made plenty of friends and almost formed a chorus at school to use her singing ability to make harmonies.
Around 2011, the King and his family were killed in a car accident, and Cossette's father assumed the throne, making her the new Princess. She was temporarily pulled out of school, though she continued to follow her classmates' accomplishments. Rosa returned to school at some point later, where she met and befriended Ionela A. Shilage.
With the outbreak of the Lighthouse War, Cossette became known for her defense of her country's offensive war, claiming that the International Space Elevator was a violation of Erusea's national sovereignty as well as publicly denouncing Osea's actions during the conflict, claiming that the country attacks indiscriminately and has injured many civilians.
At some point during the war, the Princess visited an Erusean Air and Space Administration airfield, where Sol Squadron was based. There, she reunited with her old schoolmate Ionella, her sister Alma, as well their grandfather, Mihaly A. Shilage.
Eventually, with the fall of Farbanti to the Osean forces and the collapse of the Kingdom's government, she was to be spirited away from the Usean continent. However, her transport was shot down during the ensuing civil war, and she found herself stranded on Tyler Island in the middle of a furious battle between Osean forces and Erusean factions. Three days after an abortive assassination attempt that left her the sole survivor, she was discovered by straggling Osean forces, including Spare Squadron. Avril Mead, a Spare Squadron mechanic, identified her as the princess, but the Oseans took her in.
During the chaotic Osean rout, the Osean forces took in a group of civilian refugees but found themselves surrounded by radical Erusean forces. At great personal risk, the princess took a flare and marked their positions, allowing planes from the Long Range Strategic Strike Group to destroy the Erusean armor and prevent a massacre. From there, the group traveled to the International Space Elevator via commandeered ships, arriving at the foot of the Space Elevator in the city of Gunther the next day. 
Upon discovering that Erusean radicals had hoped to continue the war using the resources of the Elevator, Cossette joined the IUN/Erusean coalition's efforts to sabotage the Space Elevator's UCAV factories. Despite numerous close calls, she helped sabotage the Arsenal Bird Justice by disabling the elevator's power transmissions to its APS, allowing IUN forces to shoot it down and defeat the Erusean radicals holding the elevator. 
Rather than wait for someone to take her back down, Cossette decided to return to the surface by BASE jumping from a platform near the top of the elevator's windbreak. During this time, two advanced UCAVs attacked. A parachuting Cossette was caught in the explosion of a missile aimed at one of the Osean fighters, but survived despite losing her helmet.
Upon the end of the war, she formed a provisional government based at the elevator to assist Usean refugees fleeing continued fighting. Carrying on Harling's spiritual legacy, the princess put her international space development plan into motion with cooperation from the refugees and survivors from the EASA.
Rosa speaking to Dr. Schroeder
- Princess Cossette's name has French origins. In particular, her middle name, "Cossette", is an alternate spelling of "Cosette", best known as the name of the heroine in Les Misérables. Her pseudonym last name, "Falcinelli", is also an Italian surname. Her real last name, "D'Elise", sounds similar to the fleur-de-lis. She is the second Erusean character to have a French name after Jean-Louis Flaubert, the leader of the Megalith defense squadron.
- Cossette is stated as 18 at the time of the article (which appears in the game's ending). Exact birth date is unknown.
- According to "Rose", Rosa's father became the King when the narrator and Rosa herself entered lower secondary school, which starts at about age 11.
- "Refugees flock to Space Elevator", WAR IS OVER, GAZE
- "Rose". Aces At War: A History 2019, pages 128—133.
- Brianna Knickerbocker on Twitter. Published January 18, 2019. Retrieved May 14, 2020.
- Megumi Han on Twitter. Published September 23, 2018. Retrieved September 23, 2018.
- File:Ace Combat 7 Skies Unknown - Gamescom 2018 Trailer.
- Cutscene 14: "The UAV Factory", Ace Combat 7: Skies Unknown.
- Cutscene 13: "Harling's mirror", Ace Combat 7: Skies Unknown.
- Mission 19: "Lighthouse", Ace Combat 7: Skies Unknown.
- Aces At War: A History 2019, page 76.
- Aces At War: A History 2019, page 105.
- Cutscene 06: "The Rose Emblem", Ace Combat 7: Skies Unknown.
- File:Ace Combat 7 Skies Unknown - E3 2017 Trailer.
- File:Ace Combat 7 Skies Unknown - Gamescom 2017 Trailer.
- Cutscene 12: "Tyler Island", Ace Combat 7: Skies Unknown.
- Mission 17: "Homeward", Ace Combat 7: Skies Unknown.