Mary Sue Syndrome

Mary Sue Syndrome is a condition that may affect female World One residents who have been possessed by a Sue-wraith when exorcism is not possible, was only partially successful, or was too long delayed. It is something like lycanthropy, except that every month, the individual turns into a full-blown Mary Sue, with all the side effects of that condition. Agent Keily Shinra is a known sufferer.

To date, there is no cure, and no treatment other than isolating the temporary Mary Sue during her episodes.

Source

 * "'I Was A Sue!' One Agent Reveals Her Shocking Story!", The Multiverse Monitor, Issue Two