After the team gained Pikachu's loyalty in Waffle, Gordon and Mr Blik's adventures of Charlie and the Chocolate factory, Pikachu became extremely loyal to Ash & the adventure team and has maintained this loyalty, and while he is not always immediately trusting of strangers, he is generally friendly to humans and Pokémon alike. He acted as a guardian and big brother to Waffle, and has been seen mediating and even breaking up fights among other Pokémon, such as in Pikachu's Vacation. In Mewtwo Strikes Back, Pikachu, Meowth, and Meowth's clone were the only Pokémon not to participate in the giant battle; Pikachu stood motionless as his clone repeatedly slapped his face. Contrary to his distrusting nature, Pikachu took a liking to Kenzie very early in the movie series, and he has retained this liking of Kenzie throughout the franchise, such as when he was very happy to see her in Waffle & Babe The Scheme Team.
Personality & Development: Ash's Pikachu
During the events of "Waffle, Gordon, Mr.Blik's adventures of The Lion King 2: Simba's pride" Pikachu temporarily developed amnesia and sided with Gordon for a while. On several occasions, Pikachu has developed an "electric flu" causing him to become overcharged and extremely powerful. During these instances, Pikachu will sometimes accidentally let off electric outbursts which can be set off on anyone, including Ash & the cats. In all of these cases, Pikachu did not mean harm upon anyone.
As shown in a handful of episodes, the first being Showdown at Dark City, Pikachu has a special fondness for ketchup, but he will eat and enjoy almost any other human or Pokémon food he also drinks root beer when the cats do. A running gag in the series and movies, each time the team meets a new ally, Pikachu uses Thunderbolt to destroy a soon to be adventure team member's mode of transportation or shock the companion his or herself. This has happened to Zim, Spongebob, tails, goat, and buhduce.
Pikachu, like his Trainer, is always happy to battle or save the day. He often tries his very best, but when things go wrong, he doesn't complain or feel bad about himself, especially when Ash, Gordon or Kenzie reassures him. Ash and Pikachu are almost identical personality-wise, and thus are the perfect match for one another.