Not all yaoi is the same (for an explanation for why yaoi is not referred to as BL in America, go here). Though generally used to refer to romance, it sometimes crops up in reference to what might best be termed school-yard-relationships or adventure-stories-with-close-guy-pals, a genre that is sometimes labeled shonen-ai.
Gorgeous Carat is closer to shonen-ai than to yaoi. There is no explicit sex or even sex at all between the main characters; in fact, the exact relationship between the two is never completely clarified. They are . . . friends? lovers? companions? slave and owner? mentor (Florian is technically older) and wildcard?
It is irrelevant. Their relationship is so close, they seem to occupy the same space despite being greatly unlike each other in personality and temperament. Ultimately, however, what they do is more important than who they are.
What do they do? Jewel heists! Kidnappings! Rescues from the Eiffel Tower! Trips to the Far East! Escapes! Bondage! Murder mysteries!
The time period is the late 19th/early 20th century. The milieu is high society in Paris with excursions abroad. The tales are rapid-fire action with all the ups and downs and crazy shenanigans that make the series rather more like Scooby-Do (thank goodness) than sappy soap opera. It's fun! It's raucous! Who knows what will happen next?!
You Higuri also created the somewhat darker Cantarella series--about the Borgias. Sometimes, I think Westerners, like myself, forget that European culture/history is as fascinating to others as Eastern culture/history is to them.