On Facebook -JOIN I Antique Online.com: Collectors of Antiques and Collectibles.
Here is the link for the group https://www.facebook.com/groups/327133184409134/
Please join our FB group where YOU can post directly.
A Community For People Who Buy, Sell or Collect Antiques, Collectibles and Art
Welcome! Judging by the style of the backstamp, I'm thinking these cups were a little bit later than mid-century, maybe even the 1970's. They probably are by Ana Fosen, but I have no documentation to back that up.
Carole Bess White
Correct spelling is TOSEN Craft. Interesting article by young Canadian entrepreneur who started this company some 10 years ago. He collects MCM, Eames era, Modernist items world wide and resells them. He seems to specialize more in furniture than porcelain. Only Japanese affiliate who makes porcelain (& plastic) ware is Kenji Fujita of Japan. Didn't see your design but good probability that his company made them. Here is link. You might contact Tosen Craft for more info.
Contact, Archives, etc. in link are very dim but provide much information.