Hi my Mum has atea set which features japanese woman in the seat of the cups, more visible when held up to the light, not painted but moulded in the design of the cup. She says it came from Japan when Dad was there from his army days. But its only mark is 'Unity' which doesn't sound Japanese to me.
The encapsuled "pictures" are called lithophane (alternatively: lithopane). "Unity" is indeed a peculiar name for such items but there are various possibilities: if "army days" refers to WW2 for example we could be talking about a "PK Unity" set made by the Kahla factories in Thuringia/Germany. Got a picture of the mark?