"Ben 10 & Generator Rex" follows Ben Tennyson, who has retired from heroics to go to college with Gwen, Kevin and Julie. His quiet life is disrupted when Azmuth, creator of The Omnitrix, reveals that the universe is doomed to be destroyed as Vilgax has the power of Maltruant. To save his world, Ben brings Gwen, Grandpa Max and Kevin and travels through the universe to recruit Rex who is currently wallowing in regret. The team must team up to fight The Forever Knights, Van Kleiss and Vilgax to prevent the destruction of Ben’s reality.
The plot serves as Ben and Rex's official integration into the DCU and a finale to the original Ben 10 and Generator Rex timeline, culminating in a mission that ultimately saves his world and allows him to reunite with his friends and family.
