The two are in stark contrast to their personalities, as Mitzi is fair and logical, whereas Kato is enthusiastic and carefree, even talking like a kind teenager.
They appeared in "Yapper", where Lilo registered Stitch in the dog show competition to show Mertle and her "dog" Gigi that they were not "riffraff". They also believed that Stitch was a rare breed known as a "blue-furred ectoplasmic detection dog that ancient Egyptians used to contact their mummy relatives in the underworld." Kato even referred to him as "blue dude". They also didn't know that Gigi was an experiment as well.
During one of the performances in the dog show, Stitch gets into a fight with one of the contestant's dogs after the latter sniffed him, to which Kato finds amusing and compares it to pro wrestling. Later, during the agility course, Mitzi shows high hopes for Gigi taking first place, though Kato comments that Gigi has the looks-like-a-rat-in-a-wig category sewn up. He even questions if they "breed" them like that on purpose or if Gigi is some kind of mutant. When Stitch came up, they were impressed by his performance, especially Kato. Also, when the dogs were inspected for being best in show, Kato openly cheered for Stitch.
When Lilo and Stitch lose the competition after Mertle switched Stitch's water bottle with a bottle full of extra strong coffee, Gantu bursts into the premises, to which Kato believes that he was another breed of dog. When Lilo and Stitch are almost hit by Gantu's plasma gun, Kato was amazed by the "laser fight" and asks Mitzi how they teach a dog to do that. This prompts Mitzi to leave, declaring that Kato has no respect for dogs, even though he assures her that he loves dogs. After Stitch defeats Gantu and rescues Gigi, Kato cheers for Stitch, which made a few other competitors cheer for him as well.