Very easy achievement that can be done at the very start of the game but can be done later so don't worry if you missed it
Right after you take control of Juno, you will walk forward and talk to the NPC, after you're done, head through the door
Now, as soon as you enter the next area, hug the wall to your right and enter the first alcove and go through the pathway
You'll be in a circle area with a pond in the center, over to your right you'll see the chest with the Fish Food.
Simply open the chest, get the food and equip it, then just toss some in the pond for the fish
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