Chotto Kawaii Iron Maiden

From MangaHelpers: Muto Yuzuki was ready for a whole new life and a different self when she got to middle school but she didn't expect it to be literally torturous. Yuzuki is “persuaded” by an upper classman named Funaki Aoi to join the Torture Club on campus which has been secretly training students to enter the field of military and police organizations as interrogation experts. Aoi sees something inside Yuzuki and thinks she might be a prodigy in torture methods. Naturally, Yuzuki wants nothing to do with such vulgar conduct but the more she spends time with the club, the more she starts to realize her own dark potential.