[@MelonHead]
Let's say a character has an insecurity, Shin's own face works nicely. If someone intentionally jeered at his face, it would be very distracting. Frustrating and if they went out of their way to harm his face worse, it would set him on a tirade.

The emotional aspect of fights is too often ignored. That's why Shin wears the mask. None of his other injuries are bothersome, but the facial disfigurement is humiliating. Especially since it's his greatest failure.