Trinity Seven: The Seven Magicians 4

 is the fourth volume of the Trinity Seven: 7-Nin no Mahoutsukai  series written by Kenji Saitō and illustrated by Nao Akinari. The volume was released in Japan on September 6, 2012 by Fujimi Shobo and currently slated to be realeased in the US on February 23, 2016.

Yen Press
One of Trinity Seven's own members, the fiendish Liese, attacks Arata with a "passionate kiss" that purloins all of his magical powers! With the Demon Lord Candidate's magic in her possession, Liese's powers are unmatched. But the key to defeating Liese must lie with the Demon Lord Candidate himself! How will Arata bear up under cruel and unusual training?! It's Volume 4 of this romantic comedy and sometimes-serious wizard school story!

Chapters

 * 13. Top Security & Trickster
 * 14. Special Training & Big Event
 * 15. Paladin & Book of Astil
 * 16. Spell Succeed & Lost Technica
 * 17. Last Crest & Problem Solving