Japanese tea set, Karatsu Yaki?

This small tea set was purchased at a Mitsukoshi department store in Japan in the mid 1990s. I do not know which store, though. I have seen another set which is identical, but it has a larger pot (selling for $530 plus shipping!). There are also a couple of loose cups on ebay. The mark on the pottery is very odd. There are three dots arranged in a triangle with a line at the base of the triangle and a circle around these marks. This is most likely Folk Craft pottery. The other set was described as Mingei, which I guess fits if "Modern" is added to the front of that word.

I contacted the seller of the loose cups on ebay in Japan, but they did not know who made this pottery, saying that the mark was basically nonsense and they did not have the box. Both completes sets came in a mass produced tomobako with stamped writing. So, I sent them images of the lid of the tomobako, including enhanced closeups of the stamps, and heard no more from them. The modest price they were asking for the cups did not skyrocket, and the description did not change, so I assume that any identification based on the writing on the box was not to their advantage. I had priced these sets at about $40-$50 based on a survey of other 1980s-1990s Japanese tea sets, and I think that is pretty close to their value. Only talking about value as there seems to be some confusion about how "special" these tea sets are...

Still, a nice set, though the pot in my set is very small. I don't think Mitsukoshi sold junk in the 1990s based on what I have read of their reputation and they sold mostly to Japanese who take their tea sets seriously. I guess it would be a good set for doing multiple pours of a green tea to experience how the tea changed with each pour. Probably not too good for a serving more than one or two people. I actually don't drink green tea as it is too acidic and burns my heart.

My images are not great. I blame the lighting. The next time I experience a surfeit of energy, I will try to do better.

https://en.wikipedia.org/wiki/Mitsukoshi

https://en.wikipedia.org/wiki/Mingei

"Mingei (??, "folk arts" or "arts of the people"), the Japanese folk art movement, was developed in the late 1920s and 1930s in Japan. Its founding father was Yanagi S?etsu (1889–1961)....

The philosophical pillar of mingei is "hand-crafted art of ordinary people" (?????? (minsh?-teki-na k?gei)). Yanagi S?etsu discovered beauty in everyday ordinary and utilitarian objects created by nameless and unknown craftsmen. According to Yanagi, utilitarian objects made by the common people are "beyond beauty and ugliness". Below are a few criteria of mingei art and crafts:

made by anonymous crafts people
produced by hand in quantity
inexpensive
used by the masses
functional in daily life
representative of the regions in which they were produced."

UPDATE: I have now seen similar pottery described as Agano ware.