Red captured Pika at Pewter City near the beginning of the Red, Green, & Blue arc. Pika had been causing havoc at the market, evading capture with his electric attacks and eating the shops' food. After his capture, Red identified him as coming from Viridian Forest. Pika was initially antagonistic towards Red, but throughout their long journey together, he soon became one of Red's closest companions and one of his most adept battlers. At one point, he was accidentally traded to Blue, who taught him a variety of non-Electric-type moves, including Substitute and Toxic.
Pika using MegaVolt on Lance
In the Yellow arc, he was the only one of Red's Pokémon to escape from the KantoElite Four, and later joined Yellow to help search for Red. During this time he learned to manipulate the decoy created by Substitute into a surfboard, which allowed him to use the move Surf. Eventually, under Yellow's command, it was able to deliver a devastating MegaVolt and defeat Lance, the leader of the Elite Four of Kanto. Before this, Red had reunited with his allies and defeated Bruno, and took Pika back under his wing after a long period of separation.
He temporarily joined Yellow's team again in the Gold, Silver, & Crystal arc when Red went to heal himself at the hot springs of Mt. Silver. Mating with Yellow's Chuchu, he produced an Egg at the Goldenrod Daycare Center, which hatched into a Pichu. He was, however, later brought to Mt. Silver when he and Gold went there to train.
Pika wouldn't make many notable appearances the next time he appeared, but served crucial roles in the FRLG arc, particularly against Deoxys.
In the ending to the Emerald arc, it is revealed by Gold that Pika wasn't inside his Poké Ball during the Pokédex owners' petrification, but, instead, able to escape, making this the second time Pika had a near-fatal experience (the first being when he escaped the Elite Four while Red got frozen by Lorelei's ice cuffs). Pika is seen wearing Red's hat and using Surf to get to the Battle Frontier to see Red get recovered, while Chuchu is seen using Fly to get to the same destination (wearing Yellow's straw hat). Gold uses this sighting to attempt to convince Emerald to wish upon Jirachi for the restoration of the Pokédex owners.
Contrary to the mechanics of the games, Pika learned Volt Tackle along with his partner and offspring without breeding. All three showcase this by using Volt Tackle against the fake Kyogre.
Red relies heavily on Pika, and has used him against many major opponents including Giovanni and legendary Pokémon such as Mewtwo and Deoxys.
The variation of Red that appears in Generation II has a level 81 male Pikachu, which is his highest-level Pokémon. It was also the highest-leveled Pokémon owned by an NPC in the entire series, but has had that title taken away by three of the rival's Pokémon in Platinum after defeating Sinnoh's Elite Four twenty times. It also appears in Pokémon HeartGold and SoulSilver, now at level 88, effectively regaining this title. Red also uses Pikachu during the Pokémon World Tournament, where it has a varying gender, and is set at level 50.
