The Hidden Power Under the Stage: After Defeating the Demon Lord and Rejuvenating, I'll Support the Academy from the Shadows

The heroic group, facing the Demon King, is plunged into a deadly situation due to the terrifying abilities of the great demon Ashtarte. However, the warrior monk Sakuya manages to capture Ashtarte by means of the art of the stone tablet and defeats the Demon Lord with praise! However, Sakuya is trapped in the "Hall of Death" by the Demon King's final curse -?