Yosuke's family has a strange tradition - once every sixty years they receive an egg from a mermaid. When the egg matures his family dutifully returns it to the sea, where the whole process is then repeated. In exchange for this favor, the mer-people bless his coastal town with bountiful catches of fish and calm seas.

But as a commercial development encroach on the sleepy seaside village and Yosuke's father is lured away from tradition towards modern properity, and turns the egg into a tourist trap, what will happen to the promise their family made to the mermaids generations ago?