Since any single character can only buy certain swim suits, it
can become somewhat tedious to obtain every outfit. In order to
speed things up a little, team up with someone you know has a
costume you would want, or one that your teammate does not have
yet. Once you become better friends, anything you give her as a
gift, in this case a swimsuit, she will keep. The key is to make
sure she is at least somewhat happy with your performance on the
court. After you give your teammate an outfit, it is most likely
you will get one as thanks when you return to your room the next
evening