From Vertical:
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 merpeople bless his coastal town with bountiful catches of fish and calm seas. But as commercial development encroaches on the sleepy seaside village and Yosuke's father is lured away from tradition towards modern prosperity and turns the egg into a tourist trap, what will happen to the promise their family made to the mermaids' generations ago?

Official English