One of the quests you'll need to complete to get Kril's shell back is a Treasure Hunt. Here's how to find all three grain treasure map pieces in Another Crab's Treasure.

To complete the map, you must find three missing pieces. You get each piece by defeating three bosses. When you talk to the Konche, he will point you to the Grove, and that is your only clue as to where to go. You will get more clues as you return each map.

To get to the Expired Grove, you first have to go through the Sands Between. You’ll be warned that there’s something nearby that wants to eat you, and you’ll need to get to the floating life rafts in the sand to protect yourself. That’s actually Pagurus, a huge boss that will chase you through the sand. He’s also the one who has the first piece of the map.

This crab is quite difficult to defeat and you may want to level up before tackling it. Instead, you can do what I did and run through the sand to explore the Grove for more Crystals and Microplastics for upgrades.