The Wood Spirit is a deleted ghost from White Day: A Labyrinth Named School. It was eventually removed for unknown reasons and it's textures were leftover in the data files.
Although not much is given according to the script, this ghost was used during the ghost tree battle. Implying that the Wood Spirit is actually Hee-Jin. However, the ghost was nulled (not reading the line) out. It's set to appear when the ghost tree appears and remain there for good. As none of the scripts said to destroy the line. There's a unfamiliar npcs object class which was never used in the game. Presumely that it was used for another ghosts. Adding the ghost does not spawn the ghost at all.
Speculation / Notes
- It bears strong resemblance to Hee-jin whom spirit appears running around the tree seeds during the boss fight.
- Judging by the texture filename, it is speculated that the wood spirit is Hee-jin and will appear after you defeated her.
- Wood is a possible reference to the Wood Amulet.
- Looking at the script, she only appears when the tree ghost appears and will remained there for good.