I can see the issue here. You have found the In Character thread, where accepted players can post as their characters. All of the information you may need is in the OUT OF CHARACTER THREAD. It is perfectly fine to join, as there isn't really a set storyline, so feel free to jump in whenever! As for relatives, I'd be just fine with that. You'd want to be related to Aria, as Koto isn't exactly a complete puzzle. Of course, Aria wouldn't know it that much. But go ahead and post a sign up, and enjoy the Roleplay!
For replying, go to the other users profile. Many people mess up on that at first, even I did. I'm on almost all day, so feel free to contact me whenever.