Hey there! Welcome back! I'm newish here my self. Just joined about a month or so back. 

I joined with a group that rps here. It's kind of sandbox like you mentioned with the one piece. We've got lore for one big medieval fantasy world. For everyone to rp in. 

But the theme is Isekai. So you don't have to know all the lore of the get go. You can just make a character from modern day earth (or whatever you want) and throw them in. 

If you're interested at all throw a message my way. 

Otherwise welcome back again! And happy roleplaying!!