Watch Ame wo Tsugeru Hyouryuu Danchi - Full movie

Sixth-graders Kousuke and Natsume grew up in the same apartment building as childhood friends. During summer break, while playing in the apartment building that is set to be demolished, they find themselves caught in a strange phenomenon. All they can see around them is a vast sea. Will Kousuke and the others make it back to their world? A journey of farewells in summer has just begun.

(Source: Netflix)