Kenkô zenrakei suieibu umishô(2007)

A boy named Okiura Saname, who was very fond of swimming, encountered a very scary mermaid when he was swimming as a teenager, and this caused him not to pursue swimming again, contrary to his inner desire, but despite this, he is now in the conservatory and the leader of the school's swimming team. One day, a girl with green hair enters their island from the middle of the sea with a floating house. This girl, who loves swimming, joins the school's swimming team and...