Gwen Tennyson and Kevin Levin

Gwen Tennyson and Kevin Levin are one of the main couples alongside Ben Tennyson and Julie Yamamoto. The pairing is also known as "Gwevin". The pairing is canon as well.

Original series
When they first met, Kevin was a renegade 11-year old, who knew Gwen as Ben's smart-mouthed cousin. He later had an vengeance against Ben and almost burnt Gwen in the episode Framed. In Back With a Vengeance, Kevin holds Gwen hostage so that Ben would give up the omnitrix. Ultimately he gets trapped in the Null Void.

During the series it is evidently displayed that Gwen feels sorry for Kevin having to live the hard life such as in Perfect Day and other encounters they have. There wasn't much or barely any interaction between the two though.

Alien Force
In Ben 10: Alien Force, there was instant chemistry. Gwen's previous pity and admiration of Kevin turned to infatuation then love. In season one and two we see the two falling for each other. The problems they have or issues did get in the way because both of them cared about each other. In What Are Little Girls Made Of?, Kevin didn't want Gwen to go off leaving him and Ben. The two also work well in the battle field. Whenever Gwen's knocked down in a fight Kevin would automatically be by her side helping her up and so is otherwise. Both of them would also put their life at risk in order to protect the other. Arguments between Kevin and Gwen are quite unique. Shouts were rare but instead talking sternly but quietly in each other's face makes up for it. In Darkstar Rising, Gwen tries to comfort Kevin for his father's absence and his stripped privelege. The two almost kiss until a Highbreed barged in. Their relationship grows in the second season. They danced together in Save the Last Dance. When Kevin gets mutuated after he and Ben try to hack the Omnitrix, he tries to break off things between himself and Gwen during his bouts of self-consciousness. Kevin was quite depressed, he also gave Gwen a "keep me in your memory" locket telling her to remember his old self before the accident in Fool's Gold. His appearance didn't bother Gwen but it proves just how much he cares about it. As seen in the episode In Charm's Way, Kevin still strives hard, though he vents his frustration in the wrong way (on Gwen) thus falling for Charmcaster which made conflict. In the end, Ben tells Kevin that Gwen's been working day and night to find a cure for him leaving him to regret getting mad at her. However, he tries to make it up to her by saving her from Darkstar in Trade-Off leaving him from human form into his mutation. Gwen though still cares for him just as much such as in Time Heals and Vendetta where she'd go to desperate measures to make things up. In The Final Battle: Part 2, after Kevin returns back to normal, they share an on-screen kiss, also reviving their relationship.

Ben 10: Alien Swarm
In Alien Swarm it also looks like they are dating. Seeing how Ben doesn't get what Gwen sees in Kevin. Gwen also kissed Kevin on the cheeks seeing how he found the chips.At the beginning of the episode he also briefly protected her from the chips. And Kevin also kissed Gwen on the cheek because she was a little jealous of Kevin building Ben a car and not her.

Ultimate Alien
In Ben 10: Ultimate Alien, for the first few episodes, they both don't show much interaction, and have a lot of arguements such as in Video Games and the early episodes. However, things got settled and changed in the episode Too Hot To Handle after Gwen gets hit by P'andor's blast, he quickly held her, helping her get up, and told her not to ever do that to him like that again. Later on the episode, he made Gwen leave the power plant because he's worried about her. In Fused, after Gwen casts the spell, she nearly fainted and landed on Kevin's lap. There was some obvious eye contact too. In the episode Hero Time, it is shown that Gwen does not approve on Kevin falling for other girls instead of her. For example, Gwen threatningly told Nocturne that she would "peel her like a grape" after seeing Kevin quite happy of Jennifer thanking him for saving her life. In the episode Ultimate Aggregor Kevin kissed Gwen on the cheek after she took him to one side to talk to him, when Kevin reveals the insanity of Osmosians when they absorb energy, Gwen discovers that it why Kevin was so bad that Kevin was a child. In Map of Infinity Gwen is defeated by Aggregor and Kevin help she, soon Kevin is defeated too, when the two up, the two embrace, Ben, Gwen and Kevin are in search of Map of Infinity, where Gwen collapses under a gate that Ben and Kevin are holding the two despairing, just Aggregor takes the first part of the map, and Kevin save Gwen. In Perplexhahedron, Kevin says he wants to take care of her in front of Swampfire and admits he likes her. And after Swampfire freed Gwen from the ice, she and Kevin kiss. Then Swampfire says in disgust "Why don't you get a room?!"