21 Emon carries the legacy of the twenty-first generation heir to the Tsuzure Inn, a family establishment dating back to the Edo period under the Tokugawa shogunate. His lineage demands he uphold the inn, particularly as Earth becomes a popular tourist destination drawing interstellar visitors, forcing him to help prevent the family business from bankruptcy. This duty conflicts with his personal ambition to become a space pilot and explore the cosmos instead of inheriting the hotel.

His companions are Gonsuke, a robot originally built for potato farming who transitions into a dedicated inn assistant and accompanies him on space adventures; Gonsuke later appears in cameo roles within the *Doraemon* universe. Another key ally is Monga (also referred to as Monger), a small alien capable of teleportation and consuming virtually any substance, whose yellow coloration often shifts with his emotional state.

The character's age and visual design differ between original manga and anime adaptations. The manga depicts him as an 18-year-old with a distinct beaked mouth, set in 2018. The 1991 anime series presents him as younger, approximately 11 to 13 years old, with a more conventional appearance, shifting the timeline to a future period between 2051 and 2071.

His adventures extend into films and crossovers. The 1981 film *Uchū e Irasshai!* features his space exploration alongside Gonsuke and Monga. A later short film, *21 Emon & Doraemon: Welcome to Hotel Tsunesha*, presents a direct narrative crossover between the two franchises.