F.F., or Foo Fighters, began as a plankton colony granted sentience and personality by a Stand DISC implanted by Enrico Pucci. Tasked with guarding Stand DISCs in a warehouse near Green Dolphin Street Prison, F.F. acted as an obedient enforcer, eliminating guards or inmates who neared the storage location.

During an investigation, F.F. confronted Jolyne Cujoh and Ermes Costello. Using abilities derived from its plankton nature, it manipulated water, created sub-bodies for simultaneous attacks, attempted to drown Ermes, and pursued Jolyne. Defeated and left dehydrated, F.F. faced disintegration. Jolyne spared it, providing water and recognizing its drive for survival over malice. This act of mercy forged a deep bond of gratitude, leading F.F. to ally with Jolyne. To move within the prison, F.F. inhabited the corpse of inmate Atroe, adopting her appearance while retaining the ability to contort unnaturally or slip through barriers due to its non-human composition.

Physically, F.F. primarily maintained Atroe's form: a slim woman of average height, consistently depicted wearing a distinctive zigzag-edged cap confirmed as fabric headwear. It almost always carried a 32 oz. cup of water, essential to prevent the plankton colony from drying out and dying. Outside a host, F.F.'s Stand form appeared as a tall, dark, robotic humanoid with masculine proportions and an alien-like visage; this form later evolved more human-like features resembling Atroe after bonding with Jolyne.

F.F.'s personality evolved significantly. Initially defined by obedience to Pucci and a drive for self-preservation, it possessed high intellect but minimal life experience. Allying with Jolyne sparked curiosity, individuality, and a deeper understanding of concepts like freedom and loyalty. F.F. constantly questioned human behaviors, experimented with actions contrary to Atroe's personality, and formed a strong protective bond with Jolyne, crediting her for granting intellect and purpose. An obsession with water led F.F. to drink any moisture-containing liquid and fiercely defend its water cup. Positive experiences gradually shifted its priorities from pure self-survival to valuing companionship, culminating in self-sacrifice.

Abilities stemmed from F.F.'s existence as both Stand and Stand user. The plankton colony granted immunity to conventional physical damage. Key powers included splitting into independent sub-bodies; invading and controlling corpses to access memories and maintain disguises; manipulating water; firing plankton bullets to injure or invade opponents; and sealing wounds with plankton to heal allies. Constant moisture was essential, as extreme vulnerability to dehydration severely limited these powers. Inhabiting a host body like Atroe's provided stability but reduced agility and introduced vulnerabilities like blood loss.

F.F. played critical roles in prison conflicts: aiding Ermes Costello against Sports Maxx, assisting Jolyne against adversaries like Kenzou and Yo-Yo Ma, and inadvertently leading allies into a Pucci trap. Its development peaked during the battle against Pucci and the Green Baby. To save Anasui from a fatal injury, F.F. used all its plankton to seal his wounds, sacrificing its own life force. In the afterlife, F.F. manifested as a joyful spirit, expressing happiness at confirming its sentience and existence before ascending peacefully.