From the blog "Dergonu's blog"

This is going to be a guide on how to buy digital VNs legally on Gyutto, using Tsui Yuri ~ as an example.   This can indeed be done from a foreign IP adress, so no proxy is needed. That being said, the entire website is in Japanese, so here is a guide with pictures and steps, walking you through it. (NOTE! You must be 18+ in order to make purchases here, obviously.)     NOTE: NSFW PICTURES ON THE SITE! Link to the Tsui Yuri ~ purchase page       Go ahead and add the game to your cart, like this:     Now go ahead and click LOG IN AS GUEST. For those of you who cannot read moon runes, click the box with the big red circle. Note, should they ever change the layout of their site, just find the big box with these moon runes and click it. (NOTE AGAIN! Slightly NSFW content in one part of the picture.) Yes, I will be saying NOTE a lot in this guide. Deal with it       Now select credit card and continue. (Yes foreign credit cards works.) Now just hit confirm and move over to the purchase page. (Just ... just follow the big red circles.) And here we are at the big screen of death. Actually, what goes where is uber simple to understand, but if all you see is gibberish, don't worry. Here is the list of what goes where. (Once again, should they ever change the layout of their site, remember which one of these corresponds with what information, and fill it out.)       List of the required info in order:   credit card number   expire date   security code   Full name   Email adress. (THIS MUST BE YOUR REAL EMAIL! IT IS IMPORTANT!)   Confirm your email adress (AGAIN, THIS IS REALLY IMPORTANT.)       Now click the button on the bottom with red under it and continue.       Now it takes you to a screen saying an email has been sent, and it lists your order number etc. (You will see your email on the page, and if you managed to put in your real email, you did good. If not... Then just ... ugh..)         You will now have gotten an email with the download link and a unique password. THE PASSWORD IS EXTREMELY IMPORTANT! WIHTOUT IT, YOU CANNOT ACTIVATE YOUR GAME!   In the email there is a URL called "guest login." Click the link, and then move down and find your game. Hit download.   NOTE!   Seeing as you are a guest, you have 1 week to download your game. The game files themselves are movable obviously, so once you have them, you can put them on an external hardrive, but the download link will disappear after 1 week.   The password you got in your email WILL WORK EVEN AFTER 1 WEEK. It will be the password you use to activate the game. (EVERY COMPUTER MUST ACTIVATE THE GAME 1 TIME BEFORE USE.) So write this password down or save the email containing it.   If we look here, we can see that the text in the circle says the game download is expired, where as the one on the top, tsui yuri, is downloadable. Click the big download button of your new game.       Now, extract the game files with WinRaR or whatever. ( Copy your password to the clipboard or remember it. )   And here we are! You have your game downloaded, and only one step remains! Putting in your password and Email once. The first time you open the program, it should look like this: (Note that the .exe file will be called something different for each game, obviously.)     And now fill in the information. (THE TOP FIELD IS FOR YOUR EMAIL, THE BOTTOM FIELD IS FOR THE UNIQUE PASSWORD.)     If you did everything correctly, you will now have your game working and ready. The next time you open it up, you will not need a password to access it. (Every new IP adress will though. So, if you move the files to your work computer or whatever, you will need to activate it again using the password.)