Carnero is an inhabitant of the city of Grancel.
He's a man working at the royal city's landing port as head of maintenance. Ever since he got promoted to his current position, he's had quite a bit of bad luck, starting with the hijacking of the Linde.
Things have only gotten worse after the attack on Zeiss Central Factory and the resulting emergency measures taken by the army, which included security checks on all arriving and departing airships, resulting in massive delays.
In order to limit further delays, he and his team would do their best to get the arriving ships ready as soon as they could, but the situation nevertheless left them annoyed. It got even worse when military patrol ships started accompanying the airliners, forcing Carnero and his crew to perform quick maintenance on them too. And after the martial arts tournament, the airliners are grounded altogether, forcing him and his colleagues out of their workplace, much to their frustration.
Fortunately, the Intelligence Division's coup gets thwarted, leaving him and his team to resume their work again.
After the Royal Guard was accused of treason, their flagship, the Arseille, was grounded in Grancel Airport and like other airport workers, Carnero was greatly impressed with the state-of-the-art airship. He mentions it's his dream to work on a similarly large project someday.
With the Birthday Celebration over, life at Grancel Airport returns to normal, which includes Carnero fumbling and getting chewed out by Tiffany over it.
While Carnero's in charge of a team of maintenance workers, he's not exactly leadership material due to his meek personality, which causes him to quickly get intimidated by people like Captain Amalthea and resented by his similarly strong-willed subordinate Tiffany, who wishes there was a real man in charge of her team.