"Powerful medicine that cleanses the body. Made from two ingredients from a D-series test subject."
The Serum (血清 kessei ) is an item in Resident Evil 7: Biohazard.
After taking the Serums Zoe makes, it will initiate the fight with Mutated Jack.
One must be used on Jack via button prompt to end the fight with him. The other is used when deciding to cure Mia or Zoe shortly after.