Yuu Koito has always been entranced with romantic shoujo manga and the lyrics of love songs. She patiently waits for the wings of love to sprout and send her heart aflutter on the day that she finally receives a confession. Yet, when her classmate from junior high declares his love for her during their graduation, she feels unexpectedly hollow. The realization hits her: she understands romance as a concept, but she is incapable of experiencing the feeling first-hand.

Now, having enrolled in high school, Yuu, disconcerted and dispirited, is still ruminating over how to respond to her suitor. There, she happens upon the seemingly flawless student council president, Touko Nanami, maturely rejecting a confession of her own. Stirred by Touko's elegant manner, Yuu approaches her for advice, only to be bewildered when the president confesses to her! Yuu quickly finds herself in the palm of Touko's hand, and unknowingly sets herself on a path to find the emotion which has long eluded her

Fifteen years ago, disaster struck human civilization, and now dangerous man-eating monsters roam the ravaged lands, posing an existential threat to the remaining survivors. Amid this turmoil, an isolated facility shelters children and nurtures them in peace. However, as a few among them find out about the world beyond the narrow periphery of their nursery's walls, their curiosity about it slowly grows.

Meanwhile, in the outside world, young survivors Maru and Kiruko band together to search for a special place called Heaven, each for their own reasons. Carrying past burdens and tragic secrets, the two hope to find answers to the cruelty they have experienced in their lives and in the world, which still remains in tatters.

The sole thing that gets the middle-aged Sasaki through his soul-sucking job is a cheerful smile from Yamada—the young woman who works at a nearby 24-hour supermarket he frequents. After every tiring day of getting berated by his boss, Sasaki stops by the store to have his spirit healed by his favorite cashier.

After a particularly grueling day, Sasaki shows up at the supermarket, only to find that Yamada's shift has already ended. Disappointed, he searches for a place to smoke when a woman from behind the store calls him over to join her. The bold and dangerously playful Tayama is quick to call out Sasaki's peculiar habit of always seeking out her coworker—even going as far as telling Yamada about Sasaki's vested interest in her.

Now, in addition to seeing his adored cashier Yamada, Sasaki also visits the store to see if his new smoking partner Tayama is around. But there is more to Tayama's mischievousness than she initially lets on. With every cigarette, an unlikely friendship begins to blossom.