Ao to Ao no Shizuku -A Calling from Tears-

The world was drowning because of unprecedented sea level rise. Thanks to science discoveries it has become possible to combat nature, and the world starts to recover.
12 years have passed. This is a story of young people born in such time. Their original village is destroyed by the sea, but they remain among those who have not fled the island. They try to live normally, play normally, fall in love normally before the sight of the ugly sea.

[From vndbreview]