Youma Bait is the derogatory term for any character in the Sailor Moon Series who seems to attract the attention of the enemy by simply existing, or is otherwise made the enemy's target (e.g. having "energy," being a potential holder of a talisman, etc.).
The most noteworthy example of Youma bait is Naru Osaka, who not only became entangled in the crossfire between the Senshi and the enemies on more than one occasion, but even managed to become infatuated with Nephrite of the Shitennou before he died while trying to save her. In the live-action storyline, she was also captured, turned into a comatose/agonized state, brainwashed, and injured before learning that Usagi was Sailor Moon. Even her mother was involved and was possessed by a Youma in Act 1.