"Mirai Nikki Mosaic" is a spin-off of the original "Mirai Nikki" series, focusing on the daily lives and interactions of the characters in a more lighthearted and comedic tone. The narrative diverges from the intense survival game of the main series, instead presenting slice-of-life scenarios that explore the personalities and relationships of the characters in a school setting.

The story centers on Yuki Amano, the protagonist of the original series, and his interactions with Yuno Gasai, his obsessive and protective classmate. In this alternate universe, Yuki and Yuno are ordinary high school students, and the deadly survival game involving future diaries does not exist. Instead, the manga highlights their quirky dynamics, with Yuno's extreme devotion to Yuki often leading to humorous and exaggerated situations. The school setting serves as a backdrop for various comedic episodes, where other characters from the original series, such as Minene Uryu, Akise Aru, and the Diary Owners, also appear in non-lethal roles.

The episodic structure of "Mirai Nikki Mosaic" allows for a focus on character-driven humor and interactions. Yuno's over-the-top antics, such as her relentless attempts to monopolize Yuki's attention, are balanced by the reactions of other characters, creating a comedic contrast. Minene Uryu, for instance, is portrayed as a mischievous troublemaker, while Akise Aru often plays the role of a calm and observant foil to the chaos around him. The manga also includes parodies of the original series' darker themes, reimagining them in a playful and absurd context.

Overall, "Mirai Nikki Mosaic" offers a comedic reinterpretation of the "Mirai Nikki" universe, emphasizing character interactions and humor over the original's suspense and violence. It provides an alternative perspective on the characters, allowing fans to see them in a more relaxed and humorous light.