You need to pay in order to post on 5ch from overseas IP. If you have domestic IP and provider is not blacklisted (that means no VPNs) you can post for free.
You can find more information about the premium service here: https://premium.5ch.net/
Make sure to call your bank to ensure that overseas transaction won't be rejected.
Forums, blogs, etc have been dying, in preference to modern social media platforms like Twitter, Facebook... and chat applications like LINE, Discord...