Mana didn't lose on purpose:
as for Tatsumiya... you make it sound like sniping coins was nothing. this is a universe where martial artists have lightning-fast reflexes and ridiculous strength, right? well, in that universe, some1 managed to shoot coins at a speed where Ku Fei barely had time to counter. I don't believe that could be such an easy feat you could just disregard. sure, Tatsumiya barely moved at all, but that could also come to show how much of an advantage she held during the fight.
then again... tatsumiya did lose on purpose, but we don't know how serious Ku Fei was either.