World of Rules: Identity Shop

Su Chen went to the bathroom, and when he came out, the people on his train no longer looked the way they had before he boarded. Having read plenty of novels, he instinctively called out for a System in his mind. To his surprise, he got a response and learned that he was now in a world governed by rules. The System had a shop where he could use the world's rule coins to buy an identity. But why were these identities so expensive?!