The everlong search for a slingshot.
Split into three parts due to OBS arbitrarily dropping the game audio for no reason.
I did some powering up off-camera, and in the process managed to snag four gems - three from a particularly lucky trip to a back floor, and one via fishing. I put two of them to use upgrading my characters' weapons.
I also found a better weapon for Xiao along the way - the Steel Slingshot. I turned her old Bone Slingshot into a Synthsphere and used it to power it up.
(Synthspheres can be created from any weapon once it reaches +5 rank or higher; they can then be attached to other weapons and provide a boost equivalent to 60% of the former weapon's stats. So don't throw out or sell any weapons you've invested any serious amount of time on!)