Full of experiments, making tips and fabrication steps, perfect dimensions, work with different materials, inventions..., all is clearly illustrated by numerous pictures.
Maybe you do not read Japanese (So do I...) : not a big problem, use Google Translate service. It's surely not perfect, but helps giving an idea of what is talked about.
So, browsing the pages, you will learn the wooden nose flutes fabrication (in babelish here)
as well as how to build nose flutes from tin cans (in babelish here) or from bamboo (in babelish here).
You'll discover the numerous different designs Mr. Katada invented.