would appreciate any "walkthrough" to subscribe to him in Fantia, or if there´s any English subscription site to get the last version
What about Ci-en? Its machine translation is tolerable enough to be able to register, set up a payment method, and subscribe to content creators.
After you register and log in to Ci-en, you can switch language from the "Language" button on the top-right corner of the site.
You must be registered to see the links
TO REGISTER A PAYMENT METHOD, click "My page" on the top-right corner (below the Language button), then click "Account Setting" in the left panel.
In the Account Setting page, go to "Payment method" under "Payment information".
From the Payment method page, you can either register your credit card, or purchase points from the available methods to use as currency for supporting content creators.
TO SUPPORT INUI, go to their content page:
You must be registered to see the links
Click "following" from below their profile photo,
Choose either 100 Yen or 500 Yen plan,
Choose your available payment method, and then click "Apply with this content".
IMPORTANT NOTES
1. How Ci-en payment works is that you only get non-free content for the MONTHS YOU PAID FOR.
This means that if you donate for this month (April), you still won't be able to download demos from March and earlier. You'll need to pay for each month you want to get content from.
However, once you already paid for April, for example, you have permanent access to all available content for that month, even if you subscribed in the middle of April, and even if you cancelled subscription in that same month or any time in the future.
Payment is immediately taken for the initial subscription, and then there will be a monthly charge at the end of the month or the beginning of the next month.
If you subscribed, cancelled, and then resubscribed within the same month, you won't be charged again for that month.
2. Inui's 100 Yen plan only provides update files for the previous demo, so you either need to pay 100 Yen for EACH PREVIOUS MONTH A DEMO IS RELEASED, or you can just pay 500 Yen once to get the full demo and then pay 100 Yen for the subsequent months for the updates.
Here's also the FAQ of Ci-en if you want to read more:
You must be registered to see the links