A world where it has been established that people routinely swing between slightly different parallel worlds... Koyomi Takasaki, who lives with his mother following his parents' divorce, enrolls in a local university prep school. Due to the atmosphere concentrated on studies and his social awkwardness, Koyomi is unable to make friends. One day, he is suddenly approached by his classmate Kazune Takigawa, who tells him that she has travelled from the 85th world where she and Koyomi are lovers.

Eighteen-year-old Tsukasa Mizugaki has failed his college entrance exams, but after pulling some strings, he manages to land a job at the Sion Artificial Intelligence Corporation. SAI Corp is responsible for the creation of "Giftias"—highly advanced androids which are almost indiscernible from normal humans. However, unlike humans, Giftias have a maximum lifespan of 81,920 hours, or around nine years and four months. Terminal Service One, the station Tsukasa was assigned to, is responsible for collecting Giftias that have met their expiration date, before they lose their memories and become hostile. Promptly after joining Terminal Service One, Tsukasa is partnered with a beautiful Giftia named Isla. She is a Terminal Service veteran and considered the best in Giftia retrievals, contrary to her petite figure and placid nature. Time is fleeting though, and Tsukasa must come to terms with his feelings for Isla before her time is up. No matter how much someone desires it, nothing lasts forever. [Written by MAL Rewrite]

Yuuji Kazami is a transfer student who has just been admitted into Mihama Academy. He wants to live an ordinary high school life, but this dream of his may not come true any time soon as Mihama Academy is quite the opposite. Consisting of only the principal and five other students, all of whom are girls, Yuuji becomes acquainted with each of them, discovering more about their personalities as socialization is inevitable. Slowly, he begins to learn about the truth behind the small group of students occupying the academy—they each have their own share of traumatic experiences which are tucked away from the world. Mihama Academy acts as a home for these girls, they are the "fruit" which fell from their trees and have begun to decay. It is up to Yuuji to become the catalyst to save them from themselves, but how can he save another when he cannot even save himself? [Written by MAL Rewrite]

When aliens known as the Oni threaten to invade the Earth, they promise to leave under one condition—a randomly-chosen human must win a one-on-one game of tag against Lum, the beautiful daughter of the Oni leader. The "lucky" person selected happens to be the lustful and unlucky high schooler Ataru Moroboshi. Given 10 days to attempt to grab Lum's horns, Ataru realizes how impossible the challenge is as he is faced with Lum's extraterrestrial powers. Motivated by a promise of marriage from his childhood friend Shinobu Miyake, Ataru manages to catch Lum off guard. He mistakenly grabs hold of her bikini top first, but he eventually achieves his true goal. Although the game is over, Lum misunderstands that she is the one whom Ataru wants to marry, and she decides to move in with him. The poor student constantly tries to shake off the clingy Lum while doing his best to reconcile with his desired fiancée. After Ataru's heroic feat results in such a disastrous outcome, it is questionable whether luck will ever be on his side.