Shishigami is the ancient spirit of the forest. During the day, Shishigami resembles a great stag with many antlers and the face of a baboon. During the night, however, Shishigami becomes Didarabocchi (the Nightwalker in the English version), a god resembling a human made out of stars with a long pointed face and tentacle-like spikes on the back. After Eboshi shoots off his head, he becomes a god of death which resembles a large humanoid made from a dark tar-like liquid. In his normal form, he bears some resemblance to a Kirin. In the subtitled edition, Shishigami is referred to as the "Deer God", rather than the "Forest Spirit" in the English dub.

Shishigami has a number of powers; most notably, the ability to give and take life away. Those that Shishigami deems to live, will live; those that Shishigami believes have lived enough, he takes away. This ability is so great, whenever Shishigami walks in his stag form, plants will instantly come to life at his feet, and just as quickly, they will wither and die. Shishigami gives a kiss to those from whom he takes life away, but gently nuzzles when giving life to something.

Shishigami intended for Ashitaka to live, retaining his curse, as he will still need it in the trials to come. When Shishigami regains his head and 'dies,' he still doesn't lift the curse, leaving only a tiny, harmless scar as a reminder of what Ashitaka has learned, and that hate still exists. In particular, San's inability to forgive keeps it fueled.