Renny Blaster is a beat-em-up in which the player can choose to control either the paranormal private investigator Fujiro Yarai, or a man with a mysterious past and supernatural abilities named Seishiro. The two characters have the same goal: prevent a secret organization of monsters and undead, run by a maniacal vampire, from taking control over Europe. The two characters begin with different initial stages, but continue on the same path afterwards. Seishiro is physically weaker and has a default ranged energy attack; Fujiro fights with regular punches and kicks. Both characters have access to unique elemental attacks that are activated by holding down a button. Most of the stages are straightforward side-scrolling action with boss battles at the end of each; a few areas contain light platforming elements.