In Eiyuden Chronicle: Hundred Heroes, Pieter is labelled the "carefree farmer" character and this couldn't be more accurate. He seems like the kind of guy who is just happy to be doing something he loves.
You'll find Pieter tending to a farm in the northwest corner of Werne Village. He will talk to you about food and so long as you're nice to him, selecting one of the first two dialogue options, he'll join you.
Pieter is required to establish a farm at your castle HQ. Initially, this brings in food and vegetables and after upgrades, it will bring in more.