Jinta and Meiko shared a strong relationship when they were little. When Meiko came back to life, Jinta was the only one who could see her. The note that Meiko had given to Jinta in episode 11 stated: "I love you Jinta. It's the kind of love that makes me want to be your wife~."
Satoshi was still little when his sister died from an accident. He always wanted to join his older sister whenever Menma would go outside. Menma however would tell Satoshi to stay and guard the peace of their house.