I got it!! So basically, when you start the rain event, Percy will call you. He calls after Cam notices them playing around in the rain and Deja sends a photo of them. One of the triggers for the Rainy Day event is the text message option "nothing much, u?" or also anything relating to the cloudy weather. When he asks if you want to join them in the rain, say no. After that, don't invite them to come over for soup in the same call. Avoid any option that offers them to join you, even if it feels mean jaja. If you do it right, the rest of the event will be just you, Cam and Deja chilling and playing games. Until the end of the event, they will send you a message on the groupchat with a photo of the CG.