I assume the ★ rating is given by the club, but who decides a woman’s rank—Black, Platinum, and so on?

You say you’re a male member of Universe, but weren’t you given an explanation during your membership interview? If you weren’t, either the staff failed to provide the necessary information, or you weren’t paying attention. At this rate, you may not know the rules and precautions, which could end up causing trouble for the women you meet. I think you should ask the staff to explain everything to you properly. Also, it’s called a “class,” not a “rank.”