Nagisa Yamada is a cold and withdrawn middle schooler living in a rural town in the countryside. Her mother works part-time jobs in her late father's stead to support Nagisa and her brother Tomohiko, who is a "hikikomori"—someone who is also extremely reclusive. Nagisa aspires to be a soldier for the Self Defense Force to finance both her and her family's needs. One fateful day, a transfer student by the name of Mokuzu Umino transfers into her school. She immediately garners the classes' attention for being the daughter of a renowned singer and her cute appearance. Claiming to be a mermaid, she seeks out Nagisa, the only person who seemingly harbors no interest toward her. Mokuzu declares that a storm is coming, and she wants Nagisa to be her precious friend. Otherwise, when the storm co