Kai is a character, who causes nothing but mischief.
Season 5: Master Quest
Kai appeared with Kail and Kim and challenged Ash, Brock, and Misty to a Pokémon battle and easily lost against them. But little did everyone know that they are secretly being acquainted by Jessie, James, and Meowth as part of their failing attempts to catch Pikachu and the other Pokémon in exchange for some money. When Team Rocket broke the deal, the brothers were intended to turn against Team Rocket as soon as Team Rocket on them first. But when Ash and his friends got free from the net the brothers idiotically cut open, Ash and his friends blasted both Team Rocket and the Invincible Pokémon Brothers off.
Season EX: Pokémon Chronicles
They later appeared in plotting to get revenge on Misty for blasting them off. They attempt to ruin the PIA test Misty was intending on taking, remove her title as Gym Leader, and take over the gym for themselves. In order to do that, they challenged Misty in a Pokémon battle for the title as the Cerulean City Gym Leader. But during the battle, they used dirty tactics as an attempt to win the match, such as Kim's Hitmonchan using an illegal sneak attack on Misty's Staryu and Kim having his brothers, Kail and Kai bring fourth theirTentacruels to battle alongside with Kim's Tentacruel against Misty's Corsola all at once. When Corsola was violently knocked out with the Tentacruel's Poison Sting, Misty dives underwater to rescue it while Nurse Joy disqualifies the brothers for their dirty tactics. They were not just disqualified, they received a capital punishment for Pokémon trainers who don't follow the rules: they are banned from all official Pokémon matches for the rest of their lives. Outraged, Kim orders the Tentacruels to use Poison Sting on Gyarados. Misty tried to protect Gyarados, but was knocked out unconscious. Furious at the brothers' dirty tactics and couldn't stand watching Misty and her Pokémon being bullied by them, Gyarados broke free from the cage and saved Misty's life by bringing her to the surface. Gyarados sends the brothers' Tentacruels flying with a massive Hyper Beam blast and also sent the brothers flying with a blast of Hydro Pump.