These are products which are manufactured by a family business binding company in tokyo established in 1983. Most of them need 'human touch' and so the amount of production at once is not so much.
Like the rainbow notebook, one sheet of different colored paper is added by hand to create its very beautiful gradation.

Their journals are also beautifully binded, and you could use the piece of paper for a letter paper by pulling out because of the high quality of paper. blunk inside.