F.F. can change his appearance at any time. However, her usual appearance is that of a deceased prisoner Atro, a young woman of medium height and slim build with a cap/hairstyle with notches at the ends on her head. In the anime, the spikes at the ends of F.F.'s hair protrude more than Atro's, which are held closer to the neck. Since F.F. is a plankton, she needs to drink a lot of water so as not to die, and since she is small (15 cm), she does not need to drink too much water.