Well for a time Fissoa was technically part of the Lurian Empire, or intended to be. Granted I'm not sure this lasted very long at all. I believe there was some obscure treaty this was intended as or some such.
Yep, the treaty was disputed by most members of Fissoa, but it was signed by their Grand Duke at the time. This later became a serious bone of contention.
However, so far as Pian en Luries was concerned, Fissoa was a vassal state.