Here is a Chinese porcelain service of particular (lotus ?) shape :
The squared cup actually doesn't belong to the same set, but the fact that it fits perfectly makes me wonder : was this kind of service usual during a particular dynasty, and did it have a main purpose (maybe a name) ?
Here is the stamp on the cups, apparently the two first characters are related to the palace, although probably not to high-ranking people. Update : apparently it reads "Guan jiao nei zao"/"Guan yao nei zao" ("Imperial Kiln for Inner Palace"), but the seal doesn't quite look like most of seals with this sentence : it has a different font and is sealed.