The Cast Pearl or the Blue Sea Pearl is a gleaming pearl of magic that protects the Sea Kingdom. It is the source of the barrier stones' power.
It's a gigantic pearl of protection, bearing a strong resemblance to the moon.
The Cast Pearl appeared floating above the castle, following Meikai's great sacrifice. After Meikai's death, the Cast Pearl subsequently took his place as protector of the sea. It would be the source of the barrier stones' power, stones that formed a defensive barrier around the Sea Kingdom.
Following its destruction by the hands of Syakesan, one of its other purposes were revealed: the Cast Pearl was the only thing sealing the Sea of Death away.
In one of the normal endings of Wadanohara and the Great Blue Sea, Wadanohara sacrificed herself in the same manner as her father before her, disappearing into the sea with the Cast Pearl being the only remains.
- It has been suggested in-game that the Cast Pearl may have lingering remnants of its creator, seen when Meikai post-humously grants his staff to Wadanohara.