For the first time since Wakaba's death, Ko goes with the Tsukishimas to visit to the sisters' maternal grandparents in the mountains, where they are caught in a snowstorm. While trapped in the house, he and Aoba remember his past visits and playing with Wakaba. Looking through a photo album, Ko recognizes Aoba's uncle, a famous mountain climber, but not his son, Mizuki, who is the same age as Aoba...