April 10th — the first day of school after spring vacation. Itsuka Shidou wakes up to what he thinks will be an ordinary day, thanks to his adorable little sister. But his peaceful routine is shattered when a massive shockwave erases the townscape, leaving a giant crater in its place. There, he encounters a mysterious girl who calls herself a Spirit — a being feared as a disaster that could destroy humanity itself. The world sees her as a monster, and there are only two ways to stop her: kill her… or make her fall in love. When Shidou’s sister Kotori, now clad in a military uniform, tells him to “go on a date” with the Spirit to save humanity, Shidou is thrown headfirst into a new, unpredictable era of boy-meets-girl romance — where love is literally a matter of life and death!