In the scene where The Gunman (Hideaki Ito) and Shizuka are intimate, you can see that The Gunman has had some kind of booster shot on his right upper arm that has left a scar. You see this as he takes off his shirt and then jumps into the bed.
Don't think is a booster shot but more of a bullet shot scar.
Right before the end-fight it starts to snow heavily for some reason, probably just for aesthetics. However, a thick blanket of snow covers everything except the chest filled with gold-nuggets. No snow seems to have fallen on the chest at all.
While the main character fights on a snowy hill, his opponent cuts a bullet out of the air with his sword. It shows the bullet and sword both moving in slow motion, but the snow continues to fall around them at the normal speed.