@nino103106
well, if you want to support the author, it's always good to purchase a copy and help them out. if you opt for the ebook variant, be warned that they only allow viewing the book via browser and smartphone and not downloading it (you can download it on your smartphone, but not extract the images with
legal means).
amazon.co.jp has an english language option just to the right of the search bar (click the globe and choose english from the dropdown menu). if you register your actual home country, it's likely that they'll only sell you physical volumes. using a fake japanese adress during the registration process might prevent this, but could also result in account closure. it's your risk. haven't heard of someone getting his account terminated though.
another popular option is registering with ebook stores like ebj, bookwalker, booklive etc. these are japanese only and more annoying to register. an online search might help with that.