Hamtarō is an adventurous golden hamster belonging to a young girl named Natsumi. He exhibits playful mischief, often hiding under blankets or exploring his surroundings when Natsumi is away. Physically, he appears slightly skinnier than his main series counterpart. He dons a bright red sweater for outdoor adventures but goes without it at home.

His personality blends curiosity with emotional vulnerability. He develops romantic feelings toward Natsumi, confessing his love internally despite knowing she views him only as a pet. This unrequited affection fuels jealousy toward Natsumi's classmate Shirohara, whom he perceives as a rival for her attention. He vents his frustrations to the family dog, Wanta, displaying moments of dramatic distress.

Socially, he interacts with a group of fellow hamsters called the Ham-Hams, including Bijou, Maxwell, Sandy, Howdy, Dexter, Snoozer, and Penelope (named Chibimaru-kun and portrayed as male). He demonstrates leadership during group challenges, such as devising a plan to retrieve Bijou's biscuit from a vase by mimicking a prize-crane machine. His problem-solving extends to collaborative efforts like gathering sunflower seeds.

Communication limitations exist: while his internal monologue is fully voiced, other Ham-Hams lack spoken dialogue, conveying actions through physical expressions. Humans cannot understand him, though Natsumi occasionally senses his presence intuitively.

Notable differences from later iterations include the absence of characters like Boss and Stan, altered designs (Maxwell wears a blue jumpsuit; Sandy lacks her ribbon; Howdy's apron is indigo), and Snoozer's mobility via hopping. The dog companion Wanta is white-furred, differing from Brandy in the main series.

No significant character development occurs across the OVA's four vignettes, as the self-contained stories focus on isolated adventures. His consistent traits throughout include mischievous exploration, loyalty to Natsumi, and cooperative problem-solving with the Ham-Hams.