Perhaps the plot could revolve around a new alien threat that the Justice League alone can't handle. They seek out Ben 10, thinking his unique abilities could be the key. Ben teams up with them, but there are clashes in their methods at first. Superman might not be used to Ben's more unorthodox ways of fighting. However, as they get to know each other better, they combine their powers and skills to defeat the alien menace.
One possible plot could be that the Omnitrix gets malfunctioned and starts sending out energy signals that attract the attention of the Justice League. Ben, in his various alien forms, has to work with the League to figure out what's wrong with the Omnitrix and stop an evil force that is also drawn to the energy. For example, Vilgax could team up with some of the League's villains like Lex Luthor to take advantage of the situation.
A cool plot might involve Ben accidentally being transported to the Justice League's universe. He has to prove himself to the League at first, as they are wary of this strange alien - human hybrid with a powerful device. Then, they discover a common enemy that is planning to destroy multiple universes. Ben, using his diverse alien abilities, and the League, with their superpowers, join forces to save the multiverse.
Chapter 848, "Just an Adopted Daughter", is the clearest early answer because it turns Gu Shengrong's situation into a concrete plot event. The chapter gives readers a real answer by opening on With a "snap," the old lady slammed the photo onto the table, clearly...
Look to Chapter 71 for the clearest answer. It begins with Shu Yan curled her lips with a hint of jealousy, "When can it be my turn..., keeps building through Who in this circle didn't know that Jiang Li had a thing for the..., and lands on Now they had to work on an empty stomach..
Chapter 14 is the strongest chapter-level answer because it starts from Lin Manru had a rare good night's sleep. and follows through on But clearly, Lin Manru was unable to accept that her delicate daughter had....
The best chapter pointer here is Chapter 20, "Miss Su, your defense is somewhat clumsy". It opens with Several people turned their heads upon hearing the sound and saw three... and closes on So, he turned and questioned Jiang Li..
If you want the clearest chapter reference, go to Chapter 39. Early on, Qi Tianyu had been looking forward to watching Jiang Li's drama unfold.; later, the chapter leans on But to his surprise, Wen Jiaojiao, who seemed to possess some strength,....
The best chapter pointer here is Chapter 49, "Mysticism Girl Jiang Li". It opens with My phone!!!" Jiang Yan's roar echoed continuously through the mountains in... and closes on Thinking this, Jiang Yan marched forward, pulled Jiang Li down from her....
Chapter 33 is the strongest chapter-level answer because it starts from Following the announcement, five artists respectively reposted the Weibo—... and follows through on Although Su Yinwan was considered half a goddess to him, the whole thing....
Look to Chapter 14 for the clearest answer. It begins with Lin Manru had a rare good night's sleep., keeps building through After freshening up, she specifically went to Jiang Yan's room on the..., and lands on But clearly, Lin Manru was unable to accept that her delicate daughter had....
Look to Chapter 63 for the clearest answer. It begins with During those seven days, he thought he had completely escaped from that..., keeps building through But now it seemed he hadn't., and lands on It was already past midnight, but the conference room at Xingmei....