Gatchan is a green-haired cherub-like creature with wings, small head antennae, and a gender-ambiguous baby-like body, referred to with both male and female pronouns. This character hatched from a prehistoric egg brought to Penguin Village by Senbei Norimaki during a time-travel expedition, joining the Norimaki family. Arale Norimaki named it Gadzilla Norimaki—blending "Gamera" and "Gojira"—though it remains primarily known as Gatchan. Gatchan communicates exclusively through "Gatchanism," a gibberish language intuitively understood by Arale. Personality-wise, Gatchan displays innocence, playfulness, and near-constant companionship with Arale, mirroring her naive worldview. It possesses an immense appetite, consuming almost any material except rubber, with a marked preference for metal. Key abilities include flight via wings, firing defensive "Antenna Beams" from its antennae, and natural replication. After overeating early in the series, Gatchan encased itself in a cocoon and emerged duplicated as Gatchan #1 and #2. Replication continued, resulting in at least eight Gatchans in future timelines.

Gatchan's background reveals it as an angelic agent dispatched by the God of the Galaxy to prehistoric Earth, tasked with curbing human technological advancement by consuming metal resources—preventing civilizations from reaching self-destructive levels. Senbei's removal of the egg foiled this mission. When the God of the Galaxy considered destroying humanity over this failure, observing Gatchan's happiness with the Norimakis and Penguin Village's benign nature prompted a change of heart, sparing Earth. In Dragon Ball crossovers, Gatchans appear as minor supporting characters, aiding Arale against foes like General Blue and General Tao by consuming metal objects and deploying Antenna Beams. They multiply further in future timelines, though one potential future was altered. Beyond the original series, Gatchan features in the Dr. Slump remake with blonde hair and a machine-based origin, appears in live-action commercials flying alongside other characters, and assists Arale in video games across Dr. Slump titles and Dragon Ball entries like *Dragon Ball Z: Budokai Tenkaichi 3* and *J-Stars Victory Vs*.