there are many things that left me utterly happy about gotg vol. 3, but one I haven't seen many people mention is that Peter refers to Mantis as his sister at least twice in the movie. Like obviously they are all a big found family and they call each other as such. But there's something about the aknowledgement of Mantis put in the same regard as Peter's grandpa on earth. Something about the fact that he considers her as well as a blood relative because they are both the children of Ego, and Ego raised Mantis to be a tool in the same manner he would've done so with Peter if he had the chance, and they were both taken advantage of by him. And despite all that they both went through because of Ego, they at least managed to find each other.