It isn’t bi, it is an Indigenous term meaning they are both masculine and feminine. The closest we have otherwise is non-binary or gender-fluid. But in Indigenous communities (at least historically, I’m not overly familiar with how 2-spirit people are treated currently) they were a part of the spiritual leadership of those communities.
While Warframe is a perfect example of a well done FTP model, you can buy a lot of stuff with real money in Warframe, it isn’t just cosmetics. But it has limited PVP and the community is fairly friendly, so it isn’t so much Pay-To-Win as it is Pay-To-Not-Work-Hard.