I want to present the idea that Usopp, Amy and I worked on, about the Priate & Marine theme in our forum.
The general idea:
All users are pirates, the staff is the marine (admin = f-admiral, manager = admiral, smods = v-admiral, etc.)
The Otaku of the month (must be a user) would be the Pirate King
The 4 richest users at the start of the month would be the Yonko
Both ranks would get their own colour and banner
If a user (pirate) wants to become a moderator, he would join the staff (marine), and become a shichibukai, just like in OP.
Shichibukais would be advanced users, or mods on probation.
Once a user reaches 100 million berry as bounty, he will be a Supernova, and that enables him to see additional forums.
Once we have the achievements for thread count, post count, rep count etc. we can introduce the rank "Captain". Once a user/pirate reaches Captain, he is allowed to form crews. We could offer them a customized profile pic, with their logo in the avatar (like amy and co did on FP), or that their posts have different coloured backgrounds, or usernames with a sign in it (e.g. at the end of the name), so that one can see who belongs to each crew.
Once a month, we could make some games (post games, picture games, quizzes, creative games) which would be supervised by 1 staff member, and the crewmembers could earn points for their crew. at the end, the crew with the most points wins.
The staff = Marine could participate as well from time to time. Just like in One Piece, the Marine has to display their dominance. So it would be the staff's goal to crush the competition and win the games, while the pirates try to defeat the marines. It would be a challange for the staff, since they are supposed to be very quality members, and if they participate, the reputation of the marine/staff is on the line
Actually, we have almost all of those ideas implemented by now!
Special post backgrounds for Yonko & Yonko Crew
Ranks & Achievements
Your own crew