Berenice Gabrielli

Berenice Gabrielli is a Quincy and a member of the Vandenreich's Stern Ritter with the designation "Q". Berenice is one of three Stern Ritter to confront Captain Kenpachi Zaraki during the invasion's initial stages. However, according to Zaraki's account, despite talking at great length about her abilities whilst his ears were still ringing from Jerome Guizbatt's roars, Berenice never had the opportunity to use them, as her throat was slit open as she spoke. Zaraki later carries Berenice's corpse atop his shoulders, alongside those of the others, before unceremoniously dropping it in front of Juhabach.

Though never observed, according to Kenpachi Zaraki's account, Berenice explained that her ability would cause the captain to question everything about himself. Otherwise, what the ability itself entails or actually does is unknown. (Source: Bleach Wiki)