The Sound of Christmas is an original side story set during the first half of the series and is written by Saya Matsuda, one of the anime's script writers. Set a little before Christmas, Jun Kanzato wants to celebrate Christmas Eve with his brothers and pressures Shin Kanzato to keep his schedule open for it. This leads to a misunderstanding the next day at school when Shin admits he can't have a Christmas party with Megumi Kayano, Takuro Sakakiba, Kanaru Morimoto, and Mayuri Yamazaki, who assume he's planning on spending it with a girlfriend.