Shin Hazama has shut his heart ever since the mysterious and sudden death of his mother during his childhood. With his scientist father occupied with research, he can only rely on his childhood friend, Kotori Izumi, the popular and good-natured daughter of his father's employer. At the end of their third year of high school with graduation right around the corner, Shin and Kotori finally begin to move forward together, both in life and in love. Everything falls apart again when Shin's father also suddenly dies. But before things can settle down, he and Kotori learn the secret behind his parents' sudden deaths when they encounter agents from a high-tech dystopian Japan existing in a parallel universe. Among them is Jin, Shin's "relative self," who is working against the humanoid weapons Miko and Niko. As the lives of relative selves are linked, Jin has two objectives: defend the vulnerable Shin to protect both their lives, and assassinate Kotori to end the ironclad rule of her relative self, Princess Kotoko—his mortal enemy and the killer of his parents. Confronted with this new reality, Shin and Kotori must honestly face their feelings for each other, even if the world as they know it will end tomorrow. [Written by MAL Rewrite]

Smart, refined, and strikingly gorgeous, half-Russian half-Japanese Alisa Mikhailovna Kujou is considered the idol of her school. With her long silver hair, mesmerizing blue eyes, and exceptionally fair skin, she has captured the hearts of countless male students while being highly admired by all others. Even so, due to her seemingly unapproachable persona, everyone remains wary around the near-flawless girl. One of the few exceptions is Alisa's benchmate Masachika Kuze, a relatively average boy who spends his days watching anime and playing gacha games. Despite his nonchalant demeanor, Masachika is the sole student to receive Alisa's attention. Unable to be fully honest, Alisa is frequently harsh on Masachika and only expresses her affection in Russian. Unbeknownst to her, however, Masachika actually understands the language yet simply pretends otherwise for his own amusement. As the odd pair continues to exchange witty and playful remarks, their relationship gradually grows more romantic and delightful—and Alisa might finally learn to freely convey her true feelings.

In front of a camera, roommates Mao Tsuchiya and Hisashi Ootomo make three promises: Mao must not tell anyone Hisashi is gay and in a relationship with another man; Hisashi must never fall in love or make any advances on Mao; and one must not disturb the other's "personal time." Thus begins their second year of cohabitation. However, everything starts to crumble when the film club—of which Mao is a member—wants to cast Hisashi in the lead role for their upcoming movie. The problem arises with the movie's plot, as it is about boys' love—a romance between a delinquent and the class president. Mao is adamant to dissuade Hisashi from becoming the protagonist due to their first promise; but, to his surprise, Hisashi is easily convinced by the director. After imagining Hisashi as the delinquent he is playing, Mao becomes overly conscious of his presence. He knows Hisashi is just a friend and out of his reach, but Mao cannot keep lying to himself anymore—his feelings toward his roommate may no longer be purely platonic.

Yuuta Asamura gets a new stepsister after his father remarries, Saki Ayase, who happens to be the number one beauty of the school year. They promise each other not to be too close, not to be too opposing, and to simply keep a vague and comfortable distance, having learned important values about men and women relationships from their parents' previous ones. Saki, who has worked alone for the sake of her family, doesn't know how to properly rely on others, whereas Yuuta is unsure of how to truly treat her. Standing on fairly equal ground, these two gradually learn the comfort of living together. Their relationship progresses from strangers to friends as the days pass. This is a story that may one day lead to love.