These are Hello Kitty Mini letter sets to commemorate Hello Kitty 40th Anniversary, Sanrio 2014.
80 mini letter sets in 80 different designs.
Each set consists of 2 writing paper + 1 matching envelope.
In total, there are 160 writing papers + 80 matching envelopes.
They commemorate Hello Kitty designs from each year: 1974 to 2013.
The year is printed on the envelopes, which tells the original year the design was created.
The size of letter writing paper is about 3.5 x 5 inch.
Very hard to find and collectible value.