"21 Emon: Uchū e Irasshai!" is a science fiction comedy series centered around 21 Emon, a young boy who works at his family's traditional Japanese inn, the Tsukudaya. The inn, located in a futuristic setting, caters to a variety of eccentric guests, including aliens and robots, reflecting the series' blend of traditional Japanese culture and futuristic elements. The narrative explores 21 Emon's daily life as he navigates the challenges of running the inn while encountering bizarre and humorous situations.

The story takes a significant turn when 21 Emon meets a mysterious alien named Monga, who becomes a recurring character. Monga, a prince from the planet Monga, often seeks refuge at the Tsukudaya, bringing with him a mix of advanced alien technology and comedic misunderstandings. Their interactions drive much of the series' humor and plot development, as 21 Emon frequently finds himself entangled in Monga's misadventures.

Another key character is Gonsuke, a robot who serves as a loyal companion to 21 Emon. Gonsuke's straightforward and often literal interpretation of situations adds to the comedic tone of the series. The trio—21 Emon, Monga, and Gonsuke—forms the core of the narrative, with their dynamic creating a balance between traditional values and futuristic absurdity.

The series is episodic, with each installment focusing on a new guest or scenario at the Tsukudaya. These episodes often highlight themes of hospitality, cultural exchange, and the clash between old and new. Despite the futuristic setting, the story retains a grounded focus on 21 Emon's growth and his efforts to uphold his family's legacy while adapting to the unpredictable world around him.

"21 Emon: Uchū e Irasshai!" combines lighthearted humor with imaginative world-building, offering a unique take on the science fiction genre. Its blend of traditional and futuristic elements, along with its memorable characters, makes it a distinctive entry in the realm of anime and manga.