Eh once mc gets OP enough that he can travel between worlds conveniently (which he probably will sooner or later), then Risu has no reason to be that anxious about him leaving her behind because it'd be just a trip/vacation for a period of time, and he could just bring her to his original world it'd be like a break/vacation people take to visit their hometown meet families and friends for Thanksgiving/New Year/whatever festivals and events (which probably will be shown in the story eventually as part of the happy ending I guess)...