|"There's... not much content here?"
Sojiro looks like an ordinary hedgehog, covered in brown spines. It appears to be based on the Paraechinus genus of hedgehogs.
Similar to his owner, Sojiro is shy around people (including Hifumi). It curls up into a ball whenever it feels shy. Sojiro occasionally listens to Hifumi's problems, even though he doesn't understand what she's saying.
- The author draws Sojiro with an antennae to represent himself in the afterword of each manga volumes, calling himself "Sōtarō" (Sojiro + Shotaro).