Coop and Fiona Relationship is the most famous relationship in Kid vs Kat. This has started when Fiona has included in Season 2, in Something About Fiona.
Fiona's First Appearance
In "Something About Fiona", after Kat throw's Coop's Soccer Ball into Old Lady Munson's yard, the ball returns to Coop's yard. Burt has estranged once and has scared when he sees an eye in the fence, and then Fiona appears above the fence.
During Something About Fiona
Then, Coop falls in love with Fiona, but Old Lady Munson never accepts his relationship with Fiona. During this episode, Coop always protects Fiona from Kat's evil tricks, and soon Coop kissed Fiona, with the purpose of protecting her. But when Coop's in danger, Fiona helps him in the fight against Kat. In the final of Something About Fiona, Old Lady Munson sent her to his house, escorted by the police, with the purpose of " protecting" her from Coop.
Never Cry Sheep
In Never Cry Sheep, Fiona accidentally switched Coop's present with her cousin's present. After Coop got Fiona's cousin present which was actually a purple scarf, Coop wore the purple scarf at school which caused him to embarrass himself.
You Kat See Me
Finoa was taking Growler for a walk, Coop invites them over for dinner at his house with his family and Miss Brannigan but when Kat makes himself invisible and causes trouble for Coop, Finoa and Growler helps him stop Kat but his formula makes her and Growler invisible even the shed. When Old Lady Munson asked her if Coop been bothering her as they return, She said that she hasn't seen him all night as the episode.
Board Kat
Finoa enters the stakeboard contest but knowing that Coop and Kat swiped brains, Kat in Coop's body coughs up a hairball at her and she stomps off angrily. Coop in Kat's body sees her with Klye Dustin and he enters the contest and shows her new special trick. Dennis and Fiona finally know the truth, Coop knows he'd never do anything bad to her which she complaints. Finoa sneaks Coop and Dennis inside along the machine, the two switches back again. Later they all watch Coop playing the video game as Kat got his picture in the game.
Birthday Bashed
Finoa attends Coop's 11th Birthday at the Bowling Alley, Pheobe was extreme jeaulous of her flirting together and tries to get to him first, In the end, Fiona decided to say that Coop saved Phoebe's life at the waterslide log, She likes the party and promise to be back but when Phoebe gives her the eye, Dennis uses the trophy and she screamed and run off as Coop and Fiona laugh together.
Kat of Diamonds
Finoa is taking care of Old Lady Munson after her back was broken for the week, but when Coop told her not to worry about Kat and his invention, she immediately got annoyed because she thought he was hogging all the fun of taking down an alien. He claimed he wasn't hogging; but wanted her not to get hurt, angering her even further. Their conversation is interrupted when Old Lady Munson yells, "FIOOOOOOOOOOOOOOOONA! IT'S TIME TO TRIM MY TOENAILS!" grossing them all out. When Coop asks Fiona whether she'd like to go skateboarding later, she sarcastically replies, "What if I break a nail?! Sorry Coop, I'm gonna be too busy looking after my Auntie Munson. ALL WEEK," before jumping over the fence, Coop sighs in disappointment. Coop uses the landline phone to leave a message to Fiona asking if she'd want to come along with him and Dennis to track down Kat. His message, however, is cut off just before he finishes. The pair then heads outside, and Dennis finds fresh cat prints and a stolen diamond ring and alerts Coop before putting the ring in his pocket. Coop storms ahead of Dennis and murmurs about Fiona not picking up the landline. Coop is then seen searching a forest, and suddenly hears something jumping down at him, and proceeds to fight it. After about 5 seconds, it was revealed he was fighting Fiona the entire time. They both say in sync, "I thought you were Kat!" before looking away from each other, both red in the face. Fiona tells Estelle not to worry; and that she was on its [Kat's] trail. Coop then charges in front of her and cries out, "No, I am!", but Fiona insists, "No, you're not!". Their arrogant argument continues, dashing in front of each other. They realize the reason Kat's building it - an army of Kats could use superior night vision to take over before any residents notice. The duo dashes in and climbs up the towers to the top. When Kat notices, he opens the roof of the tower. Coop and Fiona then get to the top of the blackout ring and charge right at the purple culprit, but he jumps at the last moment, making them run into each other and become very dizzy while he floats to the ground. When Dennis throws it up to Coop and Fiona. Fiona catches it, but Coop tries to take it away. Coop and Fiona are shown on top of Kat's blackout ring. Coop presses a button, but it makes the ring take a 90° turn. Fiona grabs Coop by his shirt, while he grabs the remote. They then hurriedly turn it back to normal, where Coop thanks Fiona and explains that he was the one who left the message, but she comments that her aunt confiscated her phone so that it wouldn't wake her up from her nap. As soon as she finishes her sentence, she spots Kat flying in on his prototype ring. The pair uses the 90° turn function to make him crash into the ring; then drive the ring to a compressing machine at a junkyard and jump off, leaving Kat and the diamonds to be compressed into cubes foiling his plans. Later in the end, Coop points out he didn't want her to get hurt because he liked her. Fiona then confesses that she likes him too. Coop then holds up the diamond ring he put in his pocket and says, "Fiona, will you...help me sneak the diamonds back into the jewellery store?" making Fiona elated, then a bit disappointed, because she thought he was going to propose to her. She replies yes, and then Old Lady Munson comes outside, claiming to feel better, but then spots Coop and Fiona together with the diamonds and yells "BURTONBURGER!", but this causes her to sprain her back again, meaning Fiona will have to stay even longer. Fiona looks partially distraught, but Coop laughs it off and picks up the compressed jewels and walks home.