KEN 10
Ben 10,000 is fighting Vulkanus (as seen in "Perfect Day" and "The Galactic Enforcers" ) and sends him into the Null-void.

It's Ken's birthday and his father (Ben), his friends, Gwendolyn, and his great grandpa (Max) give him presents. Ken gets a hoverboard from Max, Gwendolyn gives Ken a rock dog (as seen in "A Change of Face" and "Tough Luck" ), and an Omnitrix from Ben.

Ben leaves to go fight more crime, Ken turns into XLR8 and races with Ben. While fighting, people and aliens watch the fight (also a kid that looks like Kevin).

Ken finds out that Ben put a limiter on the Omnitrix to keep Ken from heroing on his own. So he becomes friends with Devlin (the kid who looks like Kevin). Gwendolyn talks to Ben about kids and their ways, Ben decides that the next time there's an attack, they'll fight together.

At night, someone tries to attack Ben and Ken. Ben finds the intruder is Devlin. Ben tells Ken to go to his room because he's too strong, Devlin was actually trying to free his father (Kevin) from the Null-Void. Ben had hidden the container with Max because of the incident in "Ben 10,000." Ken tries to fight on his own with Ben, but Ken fails. Devlin later retreats not able to find the Null-Void.

The next day, Ken tries to find the Null-Void on his own with Devlin, so he turns into Ditto. Ken finds the void and Devlin opens it and frees his father. Ken's rock dog tries to beat Kevin, but Kevin crushes him. Max later comes to fight Kevin. Later, Ben comes in and sees that Kevin has tied Ken and Max up. Kevin fights Ben until he's too weak to fight. Devlin tries to defend Ben, but he throws him aside. Max frees Ken and himself. Ken says only one hero could stand a chance against Kevin.

Ben still fights Kevin, but as before weakens Ben, so he reverts to human form. Ken comes in (surprisingly he is Grey Matter) and later switches in to Spitter, then Buzzshock. Ken reveals he used Grey Matter's brain to remove the Omnitrix's limiter so he can switch forms at will. Kevin grabs Ken and is about to throw him, but Devlin comes in and throws something at Kevin. Devlin explains why he freed Kevin, then they both fight Kevin. Ken turns into XLR8. Devlin and XLR8 are thrown away and XLR8 reverts back into Ken.

Ben sees what happened and turns into Way Big to crush Kevin, Kevin reverts back into human form, but is still strong. Kevin is about to kill Ben and Ken, but Devlin sends Kevin to the Null-Void.

Devlin was about to leave until Max grabbed Devlin. Ken says he should stay with him, so Devlin becomes part of the Tennyson family. Later, Ken's rock pet regenerates and is alive again. Ken asks Ben if he can use all ten thousand of his heroes, but Ben says don't push your luck.