With his parents abroad, Kimihito Kurusu lived a quiet, unremarkable life alone until monster girls came crowding in! This alternate reality presents cutting-edge Japan, the first country to promote the integration of non-human species into society. After the incompetence of interspecies exchange coordinator Agent Smith leaves Kimihito as the homestay caretaker of a Lamia named Miia, the newly-minted "Darling" quickly attracts girls of various breeds, resulting in an ever-growing harem flush with eroticism and attraction. Unfortunately for him and the ladies, sexual interactions between species is forbidden by the Interspecies Exchange Act! The only loophole is through an experimental marriage provision. Kimihito's life becomes fraught with an abundance of creature-specific caveats and sensitive interspecies law as the passionate, affectionate, and lusty women hound his every move, seeking his romantic and sexual affections. With new species often appearing and events materializing out of thin air, where Kimihito and his harem go is anyone's guess! [Written by MAL Rewrite]

Chiyo Sakura is a cheerful high school girl who has fallen head over heels for the oblivious Umetarou Nozaki. Much to Chiyo's confusion, when she confesses to her beloved Nozaki, he hands her an unfamiliar autograph. As it turns out, the stoic teenage boy is actually a respected shoujo mangaka, publishing under the pen name Sakiko Yumeno! A series of misunderstandings leads to Chiyo becoming one of Nozaki's manga assistants. Throughout the hilarious events that ensue, she befriends many of her quirky schoolmates, including her seemingly shameless fellow assistant, Mikoto Mikoshiba, and the "Prince of the School," Yuu Kashima. Gekkan Shoujo Nozaki-kun follows Chiyo as she strives to help Nozaki with his manga and hopes that he will eventually notice her feelings. [Written by MAL Rewrite]

Morita Mayu, a high school girl. She is extremely reticent and her silence and habit of looking at people's eyes straightly sometimes cause misunderstanding. The reason behind it is not because she doesn’t like to talk nor because she has nothing to say. The reason she rarely speaks is due to the fact she thinks too much before speaking, thus losing the timing to speak altogether. But she lives a happy school life with her classmates.

The second season of Morita-san wa Mukuchi that directly follows the first.