One day, manga author Shin Karino is greeted by four-year-old Kotarou Satou, his new next-door neighbor, who gifts him a box of tissues. In Karino's eyes, Kotarou is an odd kid: he speaks in an extremely formal manner, and he lives alone in his apartment—no parents or relatives in sight. But Kotarou neither seems to mind, nor wants to rely on people. Feeling sympathetic toward Kotarou's circumstances, Karino decides to follow Kotarou to a bathhouse in case something might happen to him and there he comes to understand the little boy is not so different from him. Little by little, Karino—along with the other residents of the apartment complex—grows fond of Kotarou and his antics. At the same time, Kotarou himself might have found something akin to a family in his unique neighbors.

A mysterious device crashes on planet Earth, causing a wildfire near where Gohan Son, Kuririn, Bulma, and Oolong are camping. Unable to fully save the forest, they decide to use the Dragon Balls to restore it to its previous condition. A few days later, a group of unknown warriors plant a seed where the mysterious device had crashed, sprouting a colossal tree that destroys the forest and neighboring cities in the process. North Kaio contacts Gokuu Son and tells him that this tree is the Shinseiju—a tree that absorbs all the nutrients in the planet and leaves it a barren wasteland, all the while growing a mighty fruit capable of providing incredible power to anyone who eats it. After learning of this, Gokuu and his friends try destroying the tree before it is too late, but that may prove to be more difficult than they had previously imagined.

On the 20th floor of the Tower, the Regulars who have been permitted to enter have to undertake arduous and extremely expensive tests to rank up. Most abandon hope and choose to stay where they are—but not Ja Wangnan. Wangnan is determined to reach the top and become the king of the Tower. However, he is weak and has repeatedly failed the exam, with debt collectors tailing him. In desperation, he attempts the exam one more time, only to encounter a mysterious and powerful individual: Jyu Viole Grace, a member of the crime syndicate FUG. Cursing his rotten luck, Wangnan has no choice but to form alliances with strong people, including Viole—who still refuses to be part of any team. Amid a dire situation, Wangnan must find a way to change Viole's mind to finally advance past the 20th floor, or he will never get a chance to build his legacy.

Tomoya Okazaki is a cynical delinquent who lacks ambition as he apathetically labors through high school. During his childhood, a tragedy had caused his father to seek solace in alcoholism and neglect his son. Yet, meaningful human interaction can be a benediction, as Tomoya learns when he meets the enigmatic Nagisa Furukawa. The odd girl offers a gesture of friendship to Tomoya, but he rejects the request, dismissing it as a trivial incident. However, as he soon realizes that he is encountering Nagisa more and more often during school, Tomoya drops his discompassions and befriends the girl. When he learns that Nagisa's dream is to revive the Drama Club, Tomoya decides to shed his detachment from the ordinary pleasures of life and dedicate himself to helping his new friend achieve her ambition. But what starts as a simple friendship may progress into something far more deep, intimate, and life-changing. As the pair face various hardships and afflictions, Tomoya and Nagisa gradually come to terms with the challenges of life.