The Brilliant Healer's New Life in the Shadows: Volume 6 (Light Novel) — Sakaku Hishikawa

Zenos and Lily succeed in founding St. Carmilla Academy, the first—ever school in the slums, with help from noble children. There, the shadow healer meets Roa, a young girl with big dreams of adventure and bold claims of being the daughter of the former Sword Saint. When Roa runs into trouble, she finds herself face—to—face with the current Sword Saint and vows to become her apprentice. Between this fateful meeting and a certain meddling wraith pulling strings, Zenos is drawn back into the adventuring life he thought he’d left behind.