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Hitler's Pikachu is the strongest Pikachu of all time.

Diet

Living in wooded areas, Pikachu often are found foraging for berries. Instead of climbing trees, they use small electrical shocks to release the berries from the tree, roasting them at the same time.

As pets, they can be fed a variety of processed food, available at many pet stores. Alternatively, like most Pokémon, Pikachu are tolerant to most "human" foods, and sometimes enjoy them more than the more nutritional food designed for their biology. In fact, Pikachu have been known to have a fondness of ketchup.

In the anime

Ash Ketchum has a Pikachu that he obtained from Professor Oak in Pokémon, I Choose You!, the first episode of the Pokémon anime series. It has appeared in every non-special episode since. Pikachu has also appeared in every Pokémon movie.

James used a Pikachu in the Pokémon League Entrance Exam in The Ultimate Test, but the Pikachu was defeated by the instructor's Graveler. James, after interfering with a battle Ash was having with the instructor, later tried to steal this Pikachu.

Another Pikachu nicknamed Puka was owned by a man named Victor on Seafoam Island in The Pi-Kahuna. This blue-eyed Pikachu had the ability to sense tidal waves approaching.

Ritchie also has a Pikachu nicknamed Sparky, who debuted in A Friend In Deed.

Ash gets turned into a Pikachu in Hocus Pokémon by a Pokémon magician named Lily. He reverts to his human form at the beginning of the next episode.

A Pikachu named Sugar belonging to the owners of a restaurant went missing prior to Cooking up a Great Story!. That Pikachu evolved into a Raichu near the end of the episode.

A Pikachu also had a part in Pokémon Mystery Dungeon: Team Go-Getters out of the Gate!. He was kidnapped by a Skarmory and Team Go-Getters set out to rescue him as their first mission. Pikachu provided them with some items in the battle.
In the manga

A Pikachu is one of the main characters in Pokémon PiPiPi Adventure.

A more mouse-like Pikachu that communicates through pantomime is one of Isamu Akai's Pokémon in Pocket Monsters.

Satoshi has a Pikachu as one of the members of his team in Pokémon Zensho. It later evolves into a Raichu.

Shuu's first Pokémon was a Pikachu he found abandoned in the forest in Pokémon Getto Da Ze!

Ash's Pikachu was the main character in the short-lived Pokémon Newspaper Strip.
Pokémon Special

Both Red and Yellow have Pika and Chu Chu, respectively. Pika often used to shock Red repeatedly. However, Pika becomes one of Red's most valued Pokémon.

Pikachu debuted in its own round in the Red, Green & Blue chapter, Wanted: Pikachu!. Here, Pika is captured by Red.

In the ninth Volume, Yellow is seen to have a new addition to her team: a Pikachu she had found injured in the Viridian Forest and nursed back to health. When Pika is left behind by Red on his trip to Mt. Silver, Pika joins Yellow and Chuchu on their trip to Johto.

Pika and Chuchu share a loving relationship, one that is so strong that even Jasmine noticed, prompting her to hand Yellow a slip with the Pokémon Daycare's address on it. In Volume 13, after Yellow and Wilton are brought to the Daycare after being shipwrecked, Yellow finds that Pika and Chuchu now have an egg shortly after they were "put together". The egg eventually hatches into Gold's Pichu.

Trivia
The "secret" move for Pikachu's evolution line, Volt Tackle, is actually based off of Pulseman's signature move, Volteccer. To get this move, a Pichu must be bred from a parent Pikachu or Raichu holding a Light Ball, though this can only happen in Pokémon Emerald, Diamond, and Pearl.
Pikachu and Raichu have been in all the regional Pokédexes.
Pikachu is the smallest version mascot.
In the games, Pikachu is the first Pokémon to have its cry changed-- to that of its anime counterpart. This only appeared in Pokémon Yellow.

Origin

Pikachu has physical aspects resembling several species of rodents, such as mice and squirrels. However, Pikachu most resembles the lagomorph known as the pika.

I want to kiss you but I want it too much.

:D