EcchiCredits is a contribution based currency only applicable here on EcchiDreams, and cannot be bought, sold or otherwise traded for real cash/tangible items. You earn them by contributing to EcchiDreams, such as making posts, threads and content that people react to, take part in, and such. Reporting bugs. And so on. They can then be traded for things on this site, typically from the EcchiStore such as premium membership or display name changes.