Embi is a performer with Master Payne's Circus of Adventure who performs sleight-of-hand, some musical numbers, tells stories... but mostly, is short. During the troop's command performance in Sturmhalten, he does a bit wearing a cat costume and gets off the stage in rather emphatic fashion by their host Aaronev Wilhelm Sturmvoraus and his Gatling gun.
He is from a small town somewhere in Africa and decided to travel the more exotic areas of the world, i.e., Europa. He , possibly in jest, his great age to a sacred vow he made "to see the world before he died" and which he takes very seriously. How this enabled him to keep himself young through the force of his will, or whether this is due to the agency of that to which he made his vow, is unknown.
In the print novel Agatha H. and the Clockwork Princess he adds that the individual to whom he made the vow was "The Great Devil Goddess." Additionally, it is mentioned that he is an expert player of (evidently) some version of the game Mancala.
Presumably he accompanies the rest of the Circus when they decamp to England, but this has not been confirmed as yet.