 If you liked
Nagi no Asu kara
|
 ...then you might like
Atri: My Dear Moments
|
Very similar watery setting with a similar appearance. Both have a run-down flooded school in a post-(partial)apocalypse type setting. And both are romance dramas intertwined with the characters trying to accomplish some goals. There's a bit of love triangle in Atri, while in Nagiasu it's more like a love dodecagon.