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Liking Pikachu isn't really about how popular he is or about what he even looks like. Some of us had that experience where he was just our first Pokemon, and what made the series real for us. For me the moment I got into Pokemon was being 5 years old and getting a Pikachu doll on my first day of kindergarten, then compounding that further by getting Pokemon Yellow and my very own gameboy for my 6th birthday. These little things happened to make the series in my mind, and got me to love Pokemon
TL;DR I like Pikachu because he was in all respects my very first Pokemon, and what made the game special for me