Staying true to his bird nature, Squash in Eiyuden Chronicle: Hundred Heroes loves a shiny object. That's why the perfect job for him is running the Accessory Shop for Nowa and his team to get boosts from.
Squash hangs out in The Treefolk Village by the Trading Post. When Nowa first talks with him, he mentions wanting to make his own jewelry with a sparklegem and asks if you can find one for him. To do so, wander the Dappled Forest until you fight an enemy called a Phantombird that drops one after the battle. Once you have it you return to Squash and he will be recruited and agree to go to the castle.
Once you build it, Squash will run the Accessory Shop on the second floor of the Trade Shop west of the HQ front door.