This giant creature ambushes Erin from beneath a boulder in the grasslands. It chases her with its large pincers, providing a terrifying threat that reinforces the dangers of the new world, before eventually giving up the chase.

Initially appearing as a harmless rock, it reveals itself to be a predator and attempts to ambush Erin. She neutralizes it by throwing an Amentus Fruit seed pod at it, which causes the creature to panic and attack itself, leaving it incapacitated while she escapes.

Erin briefly worries about the 'rock-crab-thing', wondering if she is safe from it within the inn and if it might prey on the local Goblins.

Erin encounters several rock crabs on her way back to the inn and successfully deters them by throwing slimy, noxious blue fruit seed cores at them.

Referenced by Erin as one of the dangerous creatures she has had to fight.