You need to pay attention to my posts!
There's a promotion where anyone who donates US$5 to the game gets the code, but in this update I've deactivated that promotion!
The reason was that I released a special (free) code that unlocks all the exclusive content!
In other words, in this update, all the content has been made available for free to everyone. If you want to find this special code, just read the endnote to this post here: https://itaguassu.itch.io/tacarasu/devlog/858820/public-update-tacarasu-v067-win...