Sewashi, Nobita Nobi's descendant from the 22nd century, sent Doraemon to the 20th century to assist Nobita and improve their family's future. In "Dorami-chan: Hello, Dynosis Kids!!", he joins a time-travel expedition to the Cretaceous period with Dorami and friends, aiming to scientifically verify if birds descended from dinosaurs and resolve an argument among his peers. This film emphasizes Sewashi's proactive engagement in group activities and scientific pursuits.

While typically a supporting character reacting to Nobita and Doraemon in the main series, Sewashi's role here is comparatively prominent, exploring facets of his personality beyond his usual narrative function. The story introduces new friends for Sewashi who serve as parallels to Gian and Suneo, distinct from his established manga companions.

Sewashi also appears in other Dorami-chan films like "Dorami-chan: Wow, The Kid Gang of Bandits!", consistently participating in group adventures involving extraordinary scenarios such as time travel or advanced technology, while anchored in his 22nd-century setting.