Ebirah was a giant, mutated crustacean living off the coast of Letchi Island. Ebirah was used as a sort of watchdog by the Red Bamboo. Ebirah kept anyone from coming or going to Letchi, as demonstrated when a few slave laborers imprisoned by the terrorists attempted to flee the island in a canoe. They didn't get very far before Ebirah appeared from underwater and devoured them. The members of the Red Bamboo were able to come and go from the island because they used a chemical called X-2. This was sprayed from their ship whenever to went to or from Letchi, and successfully kept Ebirah at bay.
What the terrorists didn't know was that a group of castaways, namely a fisherman named Ryota who was searching for his missing brother, Yata, were stranded on the island and had awoken Godzilla, who was snoozing in a cave. Upon emerging, the cranky Godzilla immediately picked a fight with Ebirah, who was driven back by Godzilla's atomic breath. Later Ebirah returned for a rematch, after having destroyed the last of the Red Bamboo's members as they attempted to flee the island by ship, due to its imminent self-destruction. The second fight between Godzilla and Ebirah was much longer, and ended with Godzilla tearing off the huge shrimp's claws and leaving him defenseless. Ebirah wisely turned and fled back out into deeper water, and was never seen again.