Pichu is a small, yellow, rodent-like Electric-type Pokémon. It has diamond-shaped ears with black edges, a black collar-like pattern on its neck, and a short, black, lightning bolt-shaped tail. Round pink sacs on its cheeks store electricity, though its capacity remains limited as a baby Pokémon. This inexperience often causes it to discharge electricity inadvertently when startled, amused, or agitated, sometimes surprising itself.

Living alone early in a forest, Pichu struggled to control its electrical abilities and felt isolated. Kangaskhan adopted it after it fell off a cliff, integrating it into her family. Pichu developed a sibling-like bond with Kangaskhan's biological offspring, sharing play, naps, and berry foraging. As Pichu grew larger, the physical strain of carrying it in her pouch became evident, prompting Pichu to voluntarily leave to ease this burden. The profound happiness and security experienced with Kangaskhan catalyzed its evolution into Pikachu during its departure.

A distinct variant, Spiky-eared Pichu, features jagged ear edges. This form demonstrated loyalty and bravery by assisting in freeing imprisoned allies, including human characters like Ash and Brock, often collaborating with other Pokémon such as Pikachu and Piplup.

Pichu exhibits a social yet mischievous demeanor, engaging in playful behaviors like touching tails with others to generate sparks—a described "test of courage." Its interactions blend curiosity with inadvertent electrical discharges during emotional states. While initially trusting and affectionate within its adoptive family, its personality shifted toward greater independence after evolving.

Its design and narrative roles emphasize themes of growth, familial bonds, and mastering innate abilities, with its evolution directly tied to emotional fulfillment rather than conventional training or battle experience.