Natsuki Ikaruga returns to his flooded hometown with nothing but the boat and submarine his late oceanographer grandmother left him, along with her debts. Diving the drowned ruins for anything to sell, he instead finds Atri, a robot built to look and feel human, sealed in an underwater coffin. Grateful to be salvaged, Atri swears to finish her creator's last order and to serve as Natsuki's missing leg until she does, giving him a companion for what becomes an unrepeatable last summer in a town the sea is still swallowing. This manga adapts the original visual novel.