Ushimitsu

Hikari is a ghost that used to be a student in PK Academy 20 years ago. She is skilled in playing the piano but passed away due to a disease 20 years ago. After dying, like most of the ghosts, she too lost her memories of when she was alive. However, she was completely attached to the piano in the PK Academy's music room due to her strong passion for it from when she was alive.

After Reita and Kusuo's persuasion, she decided to move on to the afterlife even though Reita told her she can be with the piano in the temple. The next day, her piano was taken down by the school and Reita asked Kusuo to take the piano and teleport it to his room in the temple. However, she didn't come back after that.

Trivia

 * The piano was actually owned by her family and after she died, her parents decided to donate it to the school.
 * character profile was found in the character guidebook.