Pichu is a small ground-dwelling rodent. Its fur is very short, and it is pale yellow in color. The tips of its large ears are black, and it has additional black markings on its neck and tail. Its tail is short, but still bears some resemblance to the large lightning-bolt structure it will develop later on in life. It has pouches in its cheeks, which are pinkish colored and used for storing small amounts of electricity. Its nose is extremely small, almost like a dot. It is classified as a quadruped, but many have been known to walk easily on their hind legs.
Pikachu is a short, chubby, rodent-like Pokémon with yellow fur all over its body. Pikachu's ears are long and come to a point with black tips. It has a small mouth, which resembles a sideways 3, it has black eyes with white pupils and two red circles on its cheeks. Its forearms are short and somewhat stubby, with 5 digits on each "hand" and its feet have three digits. It has two brown stripes on its back, and its tail is in the shape of Zigzag-styled lightning bolt, with a patch of brown fur at the base of the tail. Although it is technically a quadruped, on multiple occasions it has been shown to be able to stand and walk upright on its hind legs.
Besides its evolution and pre-evolution, it may be related to Marill, Plusle, Minun, Pachirisu and/or Emolga due to their many physical similarities.
In Pika and Goliath!, when Ash's Pikachu was injured, it was shown to have a heart rate of 156.
Raichu is a rather small tailed bipedal rodent. It is able to run faster on all fours. Like Pikachu, from which it evolves, Raichu has long ears and feet, and stubby arms. Also like Pikachu, Raichu has two horizontal brown stripes on its back. Its long, thin tail has a broad, lightning bolt-shaped end. Unlike Pikachu, however, it does not have fingers.
Raichu is yellow-brownish in color, with a white belly. Its arms are halfway brown, as well as its feet. The soles of its big feet are tan colored. Its bifurcated ears are brown on the outsides and yellow on the insides, and end in a distinctive curl at their bottom-most point. The electric sacs on its cheeks are yellow.