Comments of chapter undefined of Becoming a King with a Sign-in-system

here is my opinion and also a question is the yen currency the Japanese yen if not then what is its value in this world and..... in my opinion in this types of novel it better to keep the same currency to real world or else we don't know how rich is mc or the things buy like is 100 million yen he got is the Japanese yen we know or it has the same value of USD in this novel . I mean u didn't clarify anything..... like the house he bought is a really expensive house or just high end house and same with cars like he buying cars worth of 25 million that quit meshedup in valuation be be in USD or in Japanese yen one is too high and the other is too low