"My Roomie Is a Dino" centers on the unexpected living arrangement between a young office worker, Haru, and a small, sentient dinosaur named Dino. The story begins when Haru discovers Dino in his apartment one day, mysteriously appearing without explanation. Despite initial confusion, Haru decides to let Dino stay, leading to a series of comedic and heartwarming moments as they navigate daily life together. Dino, though small in size, possesses a quirky personality and a surprising level of intelligence, often assisting Haru with household chores and offering companionship.

The narrative explores the challenges and joys of their cohabitation, blending slice-of-life elements with lighthearted humor. Dino’s presence disrupts Haru’s mundane routine, introducing unexpected adventures and misadventures, such as Dino’s fascination with modern technology or his attempts to cook meals. The dynamic between the two characters evolves as they grow closer, with Haru gradually accepting Dino as an integral part of his life.

Secondary characters, including Haru’s coworkers and neighbors, occasionally interact with Dino, adding layers to the story. These interactions often highlight the contrast between Dino’s prehistoric origins and the modern world, creating comedic situations. The series maintains a light tone, focusing on the bond between Haru and Dino while subtly addressing themes of friendship, adaptability, and the importance of companionship.

The plot progresses episodically, with each chapter presenting a new scenario or challenge for the duo to overcome. Despite the fantastical premise, the story remains grounded in relatable, everyday experiences, making it accessible to a wide audience. The relationship between Haru and Dino serves as the emotional core of the series, emphasizing the value of understanding and embracing the unexpected in life.