Over the many years of pikachu,if あなた look closely ピカチュウ has been getting thinner and thinner.When it started he was this cute,fat little chunk of Pokemon,but now he's a skinny little freak.Which can only me one thing....Ash has forced him to become bulimic!
*Dramatizations*
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Ash:Jeez,Pikachu your so fat!

Pikachu:Pika?

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Ash:Loose some weight あなた fat bastard!

Pikachu:Pika?!
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Ash:No stop eating!Your just gonna get fatter!

*Ash shoves his finger down pikachu's throat to make him vomit his 食 up.Pikachu...