(at around 12 mins) One of the thugs was shot dead at the beginning of the movie, because the director Ryûhei Kitamura disliked the actor who portrayed him.
(at around 33 mins) In the scene where Tak Sakaguchi's character holds a pistol in his mouth, the director originally called for him to rack the slide with his teeth. He tried this, and broke a tooth. One of the zombies was played by a dentist, and fixed it for him.
In the aftermath of a few of the zombie fights, several zombies' butts are on fire. Director Ryûhei Kitamura did this on purpose, because he just thought it was funny.
On Post Mortem with Mick Garris (2009), episode April 25, 2018, the director revealed that the biggest part of the budget was lunches and dinners for the cast and crew.
Video game producer-director Hideo Kojima (of "Metal Gear" fame) was an extra in the film. Ryûhei Kitamura, as a friend, was later handpicked to direct Kojima's remake of Metal Gear Solid: The Twin Snakes (2004). Versus is attributed to heavily influencing the sword-fighting scenes in the game.