Here's the sketchbook of 河村光一郎 (Koichiro Kawamura), a guy who draws daily on his blog. He draws things from daily life and has collected enough to publish this book in 2010.
The art is nice and each watercolour sketch is filled with commentary (Japanese, although I've seen Chinese edition of the book). Each watercolour sketch is done in 15 minutes. There are also a few step-by-step tutorials on how he creates them.
It's interesting to see all the items drawn, some familiar, some new but all of them from a different context, as drawn by a Japanese artist.
Great book for watercolour and sketchbook lovers.
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Here's the Amazon Japan buying guide for your reference.