Sakamoto has several spots of blood on his shirt including one on his left shoulder. After Saigo helps him escape, as he walks down the street, the spot of blood on his left shoulder is gone.
When Sakamoto dives behind the couch you can see that next to his gun holster, on the back of the couch, there is a mound exactly where the squib for the gunshot is going to go off.
After the intruder shoots Sakamoto's uncle and the fight ensues, Sakamoto grabs the gun and shoots one final shot as the intruder jumps out the window. When he fires, we hear a regular gunshot, even though that gun had a silencer.