Another plot could involve a shared enemy that is a combination of a Grimm and a Persona - like entity. The RWBY and Persona characters would have to combine their skills and knowledge. The Persona characters could introduce the concept of Social Links to the RWBY world, and through building relationships, they all gain new powers to fight this strange new foe.
One idea could be that the RWBY characters enter the Metaverse from Persona. They might have to face their Shadows, which could be related to their Grimm - fighting fears or personal insecurities. For example, Ruby could face a Shadow that represents her fear of not being able to protect everyone.
Maybe the Persona characters end up in Remnant. They could help the RWBY teams with their unique Persona abilities. The Velvet Room could also exist in Remnant in some form, and Ozpin might have a connection to it. The Persona users could teach the RWBY characters about the power of the mind and how to use it in combat.
Chapter 100, "Ominous, there might be a bloody disaster!", is the clearest early answer because it turns Haunted House Adventure's situation into a concrete plot event. It opens with The barrage was about to die of laughter. and closes on Her eyes flickered slightly as she grabbed the hand..
Chapter 124, "Officially Certified 250", is the clearest early answer because it turns Wen Jiaojiao's situation into a concrete plot event. Early on, Since there were too many points cards inside Jiang Li's barrel,....
Chapter 322, "The Cold Beast Group's Treasure Hunt and the Panic of the White Dew Gu", is the clearest early answer because Yue Feng gets a payoff that changes the stakes. The chapter turns that into something concrete by moving from In the Yanglu Realm, the area not yet cleared by the army was still... to As the black blade collided with the demon sheep's horn, Xia Chuan's....
Chapter 99, "Dear Sister, Save Me!!!", is the clearest early answer because it turns Sister Li's situation into a concrete plot event.
Chapter 127, "He's Not Snobbish, Just Simply Bad-Tempered", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event.
Chapter 335, "Songyang Ridge, Seven Houses Surrender, First Batch of Silver Arrives", is the clearest early answer because it pushes Ji Yang into a new phase or setting. It opens with Everyone, move to the sides and make way for the army to pass. and closes on Especially following, Xu Ning and Li Longkai's question and answer.... The key payoff is that it turns battle's growth into a concrete upgrade step and sets up the next payoff in the power growth storyline linked to Rodents.
Chapter 306, "I Believe Whatever Miss Jiang Says!", is the clearest early answer because it turns Jiang Cheng's situation into a concrete plot event. Early on, But Jiang Li seriously shook her head, "No, Aunt Zhou, this matter....
Chapter 192, "He will definitely not let go of this detestable woman!", is the clearest early answer because it turns Jiang Cheng's situation into a concrete plot event. It opens with Jiang Shixu had never imagined that Jiang Cheng, who had been so...
Chapter 331, "Zhu Shun, Huang Tianxi, the Third Cold Yuan Banquet of Great Xia, and Xia Yuzong", is the clearest early answer because it turns Zhu Wen's situation into a concrete plot event. The chapter gives readers a real answer by opening on Inner City's main street, Zhu Shun led his wife Huang Yuniang and... and ending on But later, as the Camp Supply Department sent over the ceremonial....
Chapter 197, "Dear Brother", is the clearest early answer because it turns Director Sun's situation into a concrete plot event. It opens with Seeing that no one cared about what she said, Su Yinwan immediately... and closes on Wen Jiaojiao, aren't you underestimating me?.