Sometime after the events of Ultimate Alien, Kevin and Gwen left Bellwood, as Gwen went off to college, and Kevin found a home and a job near campus so he could be close with her but not without chasing and taking down Zombozo together as a team one last time. He also tells Ben that he has a new con running and asks Ben to hide him from Princess Looma and reveals that he fought, and defeated, her when he was 14 and traveling with Argit to get an engine for his car and ended up having to marry her in 3 years. This not only caused Gwen to become angered at keeping this secret (and giving Looma a decent thrashing), but Kevin kept quiet about the man who next defeated Looma would have to marry her; the end result was Ben getting engaged to her. Satisfied that one more thing from his past won't be haunting him anymore, Kevin left with Gwen in his car, much to Ben's irritation, muttering "Kevin is so dead".
In Showdown: Part 2, he was later recruited, along with Gwen to find Ben, who had vanished after destroying Pakmar's business again. He ended up on Galvan Prime MK II, where he prepared to help Ben fight Malware. However, he ended up having to fight off Khyber's former dog. During this scuffle, Kevin managed to tame it and learn its gender was female. Having taken a liking to Kevin over Khyber, the dog decided to stay with him instead. Kevin resumed his life as normal, but with a new pet to add to his responsibilities.
Kevin made another appearance in The Frogs of War: Part 2, along with Gwen, Rook, and Argit, being a part of the resistance force that was still going against the invading Incursean army. With the help of Ben, who managed to return in his new Incursean form Bullfrag, the team manages to rescue Max along with Driba and Magister Patelliday and free Earth from the Incurseans.
Kevin makes a cameo in Mud Is Thicker Than Water, in which Gwen tells him and Rook to enjoy the auto show, and they drive off.
Kevin has a main appearance in the following episode, OTTO Motives. The first is a flashback showing him and Argit attempting to move and bring objects together in the Null Void, and they both complained of its difficulty. Otto appears before them, saying that he would use the objects to help them escape the Null Void. They create a device, and turn it on. Otto, however, escapes without them, leaving them dismayed and betrayed.
The second is the current times, in which Kevin and Rook arrive at Khoros to attend the auto show. As they walk around, they soon cross paths with Argit. While they think he is up to no good, the three team up once they find Otto, saying that they waited 5 years to get their revenge. They head towards him, but they are thwarted by Otto's Violet Offenders. Afterwards, after a long struggle, and a call to Ben, they defeat Otto after a fight between Upgrade and Otto, who became merged with a series of cars to become a giant robot.
Kevin makes an appearance in Mystery, Incorporeal, in which he arrives with Zed to Friedkin University. He eventually helps Ben to fight a Stone Creature, and to investigate who was behind the attacks of the creatures. Once the team finds that it was Darkstar's doings, Ben, Rook, Kevin, and Zed fight many obstacles, including a fully-powered Morningstar. The team eventually stops him with the help of Ben as Ghostfreak.
In The Rooters of All Evil, Kevin was seen at the garage where he was eventually visited by Ben who says a group called the Rooters are after him. Kevin is uncertain on who they are but believes he should call Gwen. The Rooters eventually show up and Kevin bumped heads with the leader Servantis and remembered who he was. Kevin then escapes in his new car with Ben and decides to tell Ben what happened between him and the Rooters. Years ago, Kevin was trapped in the Null Void and said that the Rooters eventually found him. He said they then used his Osmosian powers to fuse alien DNA with humans transforming them into hybrids. This was done with the Amalgam Kids and Kevin continues saying he escaped from the Rooters and the Null Void. Kevin, with the flashback ending, says that Servantis messed with his memories and that he is a "bad guy" who is part of the Rooters. The Rooters themselves suddenly attack his car and Kevin absorbs metal while Ben transforms into AmpFibian. However, he and Ben are quickly defeated by the Rooters and are taken back to Plumber HQ. It is revealed that Osmosians aren't really aliens but are just humans with alien abilities. It is also revealed that Osmosians have different abilities and Kevin's ability is to absorb matter. Servantis is also the one that named the Osmosians and Kevin says that Servantis needs him to make a hybrid army.
Shockingly, it is then revealed that Devin Levin isn't real and was just a false memory that Servantis implanted into Max so that he will keep watch over Kevin. The Rooters being to fight against Ben and the others but Kevin manages to escape thanks to the distraction and everyone believes he won't be seen again. However, at the end of the episode, Kevin meets up with Argit in Undertown and zaps Argit with the red energy restoring his memories.
In Weapon XI: Part 1, Kevin went to Alan Albright's farm to get the young plumber to go with him. However, Swift of the Rooters soon appears and Alan doesn't trust Kevin after he almost killed him in the past. Kevin absorbs some wood in order to battle with Swift but is nearly burned by Alan due to the latter still not trusting him. However, Kevin finally gained Alan's trust again after blocking a near fatal blast from Swift. Eventually, Swift was forced to retreat back to the Null Void after getting hit by Argit's quills and Kevin shocks Alan's head restoring old memories. It was then revealed that Alan knew Kevin since they were younger and formed the original Rooters together. Kevin, at some point, left a coded letter to Gwen saying he has got Alan and that she must get Manny and Helen but not tell Ben about it. Later, Kevin is with Alan and Argit and Alan wants to help Kevin out. However, Kevin shocks Alan again triggering another flashback that shows Alan receiving his Pyronite powers. Kevin says he will go in alone into the Null Void to confront Servantis and asks Alan to take care of Zed. Kevin heads inside and eventually reaches the Rooters' base and Servantis allows Kevin to enter. Servantis is hoping to take out the "coming storm" but Kevin lashes out saying to stop calling Ben that and Ben is his friend. Suddenly, Ben, Gwen, and the Amalgam Kids arrive much to the anger of Kevin. Servantis then puts his plan into action by shocking the Amalgam Kids and turning them against Ben. Servantis then creates a forcefield around himself and Kevin and seemingly convinces Kevin to turn on Ben. Kevin thrashes Ben around (who was Kickin Hawk) who the latter was forced to retreat. At the end, Kevin rejoins the Rooters and decides to carry out his plan to destroy Ben.
In Weapon XI: Part 2, Kevin is seen with the Rooters where he is searching for Ben. Kevin is determined to kill Ben in honor of Pierce's name. During a flashback told by Argit, it was revealed that Kevin and the Amalgam Kids attacked Ben's group when they were younger. Kevin used a blaster at Ben but Ben dodged and transformed into Eye Guy pinning Kevin down. However, Kevin touched the Omnitrix symbol and mutates again. Kevin starts to go insane attacking even his own allies. Kevin was brought down by Argit's quills and he and the Amalgam Kids were taken back to the Null Void. Servantis was greatly upset at the failure and sent Kevin and the Amalgam Kids away erasing their memories of that event. Back in present time, Ben's group eventually reached the Rooters' base and Kevin prepares himself to fight Ben. Kevin was eventually confronted by Ben as Gutrot but quickly touched the Omnitrix and mutated again. Ben then transformed into Swampfire but Kevin easily contained him. Eventually, Ben was caught by Helen and Kevin took him to Servantis. When Ben woke it, it turns out that Servantis created a device that will destroy Ben and the Omnitrix at the same time. However, before Kevin could toss Ben inside, Kevin dropped Ben and picked up Servantis instead. Kevin then headbutted Servantis and then shocked the rest of the Amalgam Kids turning them back to normal. Kevin did that to stop Servantis from alternating the other's memories and turns back to normal explaining it all to Ben. Kevin tells Servantis that Ben is like a brother to him and that he will never turn on him again. Later, the Rooters are soon stripped of their Plumber status by the Magistrata and Kevin leaves the Null Void with everyone else.
In Charm School, Kevin was seen at Friedkin University working on his car. Gwen attempted to get him to come to see why Charmcaster was also at the University but Kevin said Charmcaster was her problem. However, Kevin decided to go after hearing Ben was coming as his car may get destroyed again. Eventually, Ben and Rook arrive and Kevin decides to use Rook's expertise in alien tech to help build the ultimate car that can survive anything. Kevin takes Rook into a room with numerous of advanced alien tech revealing he used his powers to harvest Taydenite in order to keep getting money (saying he doesn't have to work ever again). Eventually, Kevin and Rook construct the perfect car capable of withstanding everything. However, when a magic spell from Gwen and Charmcaster's fight hits the car, it completely disappears much to Kevin's horror. However, Kevin gets over it and helps out Gwen and Ben fight off Charmcaster and her Stone Bats. Eventually, Charmcaster was defeated and Kevin decides to go to the auto show with Rook.
In Third Time's a Charm, Kevin and Zed have taken residence in Lucky Girl's headquarters, still feeling sad about his car. Gwen said she has searched all over the universe for his car, but Kevin begs her to search once more. They landed themselves inside his car in Ledgerdomain, but Kevin gets teleported out with his car leaving Gwen stranded. Kevin calls Ben and Rook for help as he assures that Charmcaster is the one behind the situation. The three boys meet Bezel, the most powerful sorcerer of all. In the library, Charmcaster appears as she shows them that she has turned Gwen into a totem, much to Kevin's shock. The boys got teleported out and Charmcaster makes a magic barrier that prevents them from entering the library. With the help of Bezel, they were able to access the library to fight Charmcaster and her rock monsters. Zed takes the totems of Gwen, Darkstar, Hex, Adwaita, and Bezel as Charmcaster turns into a dragon using a spell. Ben and Rook then covers Kevin as he runs to his car, but the attacks from his car would not work since he does not know magic. Ben managed to trick Charmcaster by having Skurd absorb Bezel's totem, telling Charmcaster to look inside her back. Charmcaster touched the drawing that Gwen made using Charmcaster's magic from her lipstick, turning her into a totem and trapped inside her bag. Kevin is seen back in Lucky Girl's headquarters, being relieved that Gwen is safe and that she and Charmcaster can be friends under different circumstances.
At the end of the final episode, A New Dawn, after watching the universe created, Ben called Gwen to get Kevin and proposes that Ben, Gwen, Rook, and Kevin all go on a road trip to explore the universe they watched being created together.