One possible plot could be that Luffy and his crew are sailing in the Grand Line when they encounter a strange energy. It turns out to be a Dragon Ball. They then have to deal with various villains from both universes trying to get the ball. Maybe Frieza hears about it and teams up with some of the pirates from One Piece. And Goku, sensing the power of the Dragon Ball, also arrives in the One Piece world to help Luffy protect it.
A cool plot could be that the Dragon Balls are scattered across the One Piece world. Goku and his friends lose their memories and end up in different parts of the world. Luffy and his crew find Goku and try to help him regain his memory. As they search for the Dragon Balls, they encounter all sorts of enemies. Some of the One Piece villains like Doflamingo try to use the Dragon Balls for their own desires. And the Saiyans start to remember their powers slowly as they fight alongside the Straw Hats.
Chapter 389, "Slaughter Pig Platter", is the clearest early answer because it turns Xu Huiqiu's situation into a concrete plot event. A useful checkpoint is the way the scene starts with Jiang Li gave Xu Huiqiu a meaningful look and finally voiced the...
Chapter 757, "Don't come begging us then!", is the clearest early answer because it turns Lin Manru's situation into a concrete plot event. The chapter turns that into something concrete by moving from Old Man Cheng's guess was spot-on.
Chapter 730, "How Can You Make a Deal with a Madman?!", is the clearest early answer because it turns Jiang Cheng's situation into a concrete plot event. It opens with Xu Ning's emotions grew more intense as she spoke.
Chapter 847, "How Else Can You Argue?!", is the clearest early answer because it turns Zhao Lang's situation into a concrete plot event. The chapter gives readers a real answer by opening on The Rong family couple watched the situation unfold, exchanged a...
Chapter 890, "Why didn’t anyone inform me?!", is the clearest early answer because it turns Jiang Cheng's situation into a concrete plot event. The chapter turns that into something concrete by moving from Zhao Lang made a great impression on Jiang Mingchuan.
Chapter 767, "Jiang, Jiang Yu?!", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. The chapter turns that into something concrete by moving from Then, Zhao Lang felt a different kind of gaze and turned his head,...
Chapter 622, "Actually Tie Her Up?!", is the clearest early answer because it turns Su Yinwan's situation into a concrete plot event. The chapter turns that into something concrete by moving from Watching the uncommon expression on the man's face, Su Yinwan was...
Chapter 700, "As long as the money is in place, I am willing to do anything!", is the clearest early answer because it turns Miss Jiang's situation into a concrete plot event.
Chapter 552, "Branches, 20 Points Each, No More", is the clearest early answer because it turns Bai Lu's situation into a concrete plot event. It opens with Jiang Cheng smelled the scent and crawled out of the shed, but before...
Chapter 403, "Neither Jiang Lijiang nor Jiang Yan Came?", is the clearest early answer because it turns Jiang Yan's situation into a concrete plot event. The chapter gives readers a real answer by opening on Now our helicopter has arrived above the harbor in Yan City, and...