World 99 is a two-volume dystopian novel centered on Sorako Kisaragi, a woman without a fixed personality who survives by resonating with others and reshaping herself for each community. As the seemingly cute Pyokorun begins to alter the structure of society, the novel follows Sorako's life through unsettling questions of discrimination, exploitation, sexuality, family, memory, and adaptation.

As Sorako moves between worlds by changing the self she presents, Pyokorun shifts from a beloved creature into a force that rewrites human society itself.