An artificial island in Tokyo Bay—Kyokutou Houreigai Tokubetsu Chiku (Far East Special District), commonly known as the 24-ku (24th Ward). Childhood friends Ran, Kouki, and Shuuta, who were born and raised there, have different family backgrounds, hobbies, and personalities, but always hung out together. However, their relationship changes drastically in the wake of a certain incident. At the first anniversary memorial of the incident, the three friends happen to meet again and their phones begin to ring simultaneously. The phone call is from a supposedly dead friend, urging them to "choose the future." The three will try to protect their beloved 24th Ward and the future of its people in their own ways.

Forty-four years ago, the surviving nations of the Valbanil War declared peace and forbade the use of the devastating demon contracts that ravaged the land. Now, inexperienced knight Cecily Cambell is eager to follow the example of her family and protect the people of the city using the sword she inherited from her father. Her first challenge arises in the market. A crazed swordsman wreaks havoc upon civilians and Cecily jumps into action to restore order. Overwhelmed, her weapon shatters, but a skilled stranger wielding a strange-looking sword intervenes. With the situation diffused, Cecily heads to a local blacksmith in an effort to restore her family heirloom. However, she finds out that her savior—the blacksmith Luke Ainsworth—may be the only person capable of such intricate repairs. Determined to have her treasured sword repaired, she seeks out the man who rescued her. However, a group of bandits suddenly attack a convoy headed for the city. The assailants look inhuman, and an ice demon appears. Luke suspects the use of a demon contract and calls upon a sacred power to defeat them. Meanwhile, a shadowy hooded figure lurks, watching from a distance. Who is this mysterious evildoer, and what does his appearance mean for the pair? [Written by MAL Rewrite]

Nijiiro Days follows the colorful lives and romantic relationships of four high school boys—Natsuki Hashiba, a dreamer with delusions of love; Tomoya Matsunaga, a narcissistic playboy who has multiple girlfriends; Keiichi Katakura, a kinky sadist who always carries a whip; and Tsuyoshi Naoe, an otaku who has a cosplaying girlfriend. When his girlfriend unceremoniously dumps him on Christmas Eve, Natsuki breaks down in tears in the middle of the street and is offered tissues by a girl in a Santa Claus suit. He instantly falls in love with this girl, Anna Kobayakawa, who fortunately attends the same school as him. Natsuki's pursuit of Anna should have been simple and uneventful; however, much to his dismay, his nosy friends constantly meddle in his relationship, as they strive to succeed in their own endeavors of love. [Written by MAL Rewrite]

Momose, a 26-year-old office worker, recently changed jobs after being harassed by his former boss. He is concerned that his new boss will also use power harassment to make his life miserable. Momose tries to hide his concern about facing a similar situation with his new boss, Shirasaki. To Momose's surprise, however, Shirasaki's inherent airheadedness immediately alleviates all of his concerns, giving him a sense of relief.