Raichu is a bipedal, rodent-like Pokémon. Raichu is covered in dark orange fur with a white belly. Its bifurcated ears are brown on the outside, yellow on the insides, and end in a distinctive curl. There is a circular yellow marking on each cheek where its electric sacs are, and it has a triangular, dark brown nose. Its arms and feet have patches of brown fur at the end, and the soles of its long feet are tan with a circular orange pad in the center. On its back are two horizontal brown stripes. Its long, thin tail has a lightning bolt-shaped end. This lightning bolt is chipped on females. Raichu exudes a weak electrical charge from all its body and glows slightly in the dark.
Raichu's tail is used to gather electricity from the atmosphere, or it can be planted in the ground to search for electricity. It also protects Raichu from its own high voltage power. Raichu can store over 100,000 volts of electricity. If Raichu's sacs are fully charged, its ears will stand straight up and its muscles become stimulated. However, it will become aggressive if it has stored too much electricity and stress. To keep from reaching this state, it discharges electricity through its tail into the ground. This leads to scorched patches near its nest. Being the result of evolution via Evolution stone, Raichu is rarely found in the wild, though they can be found in forests and woodlands. The main reason Raichu is rarely seen in the wild is because people prefer the look it had as Pikachu. Like its pre-evolved forms, Raichu is able to learn Volt Tackle as a signature move.
In Alola, Raichu has lighter coloring and more rounded features. Its eyes are blue with yellow half-circles along the bottom. It has large yellow ears with an inner spiral toward the base and brown on the inside. These ears are thicker and less pointed than a standard Raichu's ear. In addition to its white belly, Alolan Raichu has white markings on its paws with bright yellow lines between its digits. The stripes on its back have also turned white, and there is a small, white circular marking on each heel. The lightning bolt-shaped tip of its tail has rounded edges. By collecting its psychic power in its tail, it is able to ride it like a surfboard and float in the air. While its cheek sacs are still used to store electricity, rubbing them releases a sweet aroma while also getting a light shock. This is also thought to be connected to its Psychic abilities.
Alolan Raichu's origins were initially a mystery at the time. The people of Alola suggested it ate too many sweet and fluffy pancakes. However, researchers believe the change is related to a diet resulting from Raichu eating pancakes made from a secret Alolan recipe. It is also believed the weather and climate of the Alola region played a role in the transformation. Alolan Raichu is capable of unleashing star-shaped thunderbolts. Alolan Raichu is also known by the name hodad.
A Raichu appeared in Pika and Goliath!, under the ownership of Sho, who sought to have possession of one Pokémon each from the Pikachu evolutionary line. It battled Ash's Pikachu twice in that episode, with Raichu being victorious the first time and Pikachu triumphing during the rematch.
In Destination: Coronation!, Visquez used a Raichu to defeat a Trainer's Hypno. It then went up against Ash's Pikachu, but Ash withdrew Pikachu and sent out Gengar in his place; the Shadow Pokémon then managed to defeat Raichu.
In Gotta Catch a What?!, multiple Pikachu evolved into Raichu using the Thunder Stones they had dug up.
In The Legend of Thunder!, a Raichu was one of the Electric Pokémon that were lured by the "Miracle Crystal" that Attila and Hun were using. Raichu tried to zap the crystal, but the attack ricocheted back to it.
Lt. Surge has a Raichu, which was first seen in Silph Co. in Go for the Golbat. However, it never participated in battles until fighting the Masked Man in his Mahogany Hideout, where it helped Surge break in and seemingly backed the mastermind into a corner, until his Houndour called upon dozens of wild Houndour to thwart Surge, instead. The former Team Rocket triad member barely escaped with his life after having many of his Electrode self-destruct.
Raichu originally had an evolved form named "Gorochu", which would have had two horns and fangs. Sugimori said that while there was nothing wrong with its appearance, it was nonetheless omitted, as the staff found the game balance to be better without it.
Raichu's FireRed and Sun Pokédex entries reference a 1903 documentary film called Electrocuting an Elephant by Thomas Edison.
Several Pokédex entries claim Raichu can discharge up to 100,000 volts. However, its Stadium entry claims it can only discharge up to 10,000 volts. This is likely a translation error due to the way numbers are read in Japanese, where 100,000 literally reads "ten ten-thousands".
Although Pikachu is the starter of Pokémon Yellow, it is not possible to directly evolve it into Raichu in the game, and must be traded in from Red and Blue. This inability to evolve Pikachu is a reference to Ash's Pikachu in the anime.
Raichu and its pre-evolved form both share their category name with Sandshrew, Sandslash, Rattata, and Raticate. They are all known as the Mouse Pokémon, though Rattata and Raticate have also been called the Rat Pokémon.