Dedenne dropped a berry, falling in Bonnie's hands. Later, Dedenne attacks Bonnie and Pikachu because of the berry. When Bonnie gives the berry back to Dedenne, the Fletchling that Ash will capture later on steals the berry and swallows it, upsetting Dedenne and making it run away, which tipped off Bonnie.
Dedenne came while Bonnie is petting Fletchling and steals the food. They chase it for a while. Later, Pikachu & Dedenne are being chased and harrassed by Team Rocket and James' new Inkay. Later, they become friends and look for Ash, Clemont, and Bonnie. When Team Rocket came back, Dedenne and Clemont battled against Inkay and Wobbuffet, defeated them with Nuzzle and ThunderShock, giving pleasure to Bonnie. Later, Bonnie and Clemont catch it, but Bonnie starts to carry Dedenne in her little purse.
It used its ability to detect electricity from Pikachu to find it, Froakie, Fennekin, and Chespin when the four were separated from their Trainers.
Dedenne is a Pokémon that relates to Snorlax. It can be very gluttonous, and after its meal, Dedenne goes to sleep in Bonnie's purse. In battle, Dedenne is sometimes even stronger than Ash's Pikachu.