First of all, there’s a similar community like odai_themes. It’s called odai, and it has translations of odai just like this community. However, you don’t have to claim anything. Also, I do different themes than the odai community, and I’ll be doing them often.
Think of all the theme communities out there. They had to come from somewhere, right? It most likely started with 30kisses, and then it spread until today, there are many themed writing and drawing communities where you can sign up and challenge yourself to write all of the themes presented. odai_themes is different in that you don't need to claim to take a theme set. On Japanese websites, anyuone can take the themes and use them as long as they credit the site.
What you can do is find a theme set that inspires you, post it in an entry in your journal and write fanfic or draw to them.
It's important that you credit the website that the themes originated from. I don't care if you credit my translations or not. You can use the banner provided or just link to the site through text. I'd also like if you replied to the post of themes you've chosen, as I'd be interested in seeing what you're writing. :)