This quest is available starting in Chapter 4.
Talk to the girl at the Cafe in Castle Gate Plaza (the upper right corner). She will tell you something about the ladies. Grab your crossbow and shoot Prank Bananas at the 5 ladies nearby. Talk to her again. She will be amused, but says that that may not have been truly just.
Also, if you talk to a man next to the South Gate plaza archery shop, he will comment on how she is upset when she is usually all smiles. In addition, this set-up will reappear until the epilogue, but no reward is given.