Not to be indiscreet, but it seems to me the fact that only girls can play the best mahjong in the future and the fact that they never wear panties is connected! Clearly, panties block the source of their mahjong power, which would explain why boys can't utilize it. We had Miyanaga-san, a top mahjong player, check all the girls to make sure that none of them, in fact, wore any undergarments, and our conclusion was that she's very cute when all she can do is blush and stammer.