Ayaka, the little girl in episode 11, is told by her father that Santa really exists. However, he has to go overseas on a business trip, and won't be able to make it home in time for Christmas. Another kid at school then tells her that Santa isn't real, and then she hears that her father won't make it back in time, causing her to suffer a Heroic B.S.O.D.. Then her father does come home, and shows up as Santa, fulfilling his statements from earlier.
And at the end of that episode, Sonico plays Moonlight Star (over the ending credits) during a concert, due to how important the song was to her, being both the one she heard that led her to meet Toma and the one Toma told her to practice and be able to play so she could keep the guitar Toma gave her. Toma, who was secretly in the audience, leaves Sonico a note that she earned the right to keep the guitar for her performance.