Character Analysis
We understand that most teens don't get along with their younger brothers. But when Kiriel actually makes an effort with Jason, good things happen. It helps the guy's self-esteem; he starts to feel more confident; plus, with a little encouragement, Jason even promises to go out and make some friends of his own. So while we don't actually see this last bit happen, it's definitely a start.
Best of all, though, Shaun's mom is super grateful to Kiriel for getting Jason to be more social. But you don't have to take our word for it, or even Kiriel's—she comes right out and thanks him, saying, "I really appreciate it. He has such a hard time making friends "(13.66). She worries about Jason, so as things start looking up for him, they also start looking up for her. It's the ripple effect of Kiriel's kindhearted ways.
We know that Jason's a shy kid who doesn't have any friends or hobbies outside of video games, so when Shaun (the real one, not Kiriel) constantly makes fun of him and calls him names, it doesn't help matters. Sure, that's what brothers do, but Kiriel uses his inhabitance of Shaun's body as a chance to change something around the Simmons's household, so by the time the real Shaun gets back, well, he has a new and improved brother waiting to meet him.