The Brilliant Healer's New Life in the Shadows: Volume 6 by Sakaku Hishikawa

Thanks to Zenos and Lily’s time at an academy for noble children and the assistance of several of its students, the gang is able to successfully establish St. Carmilla Academy, the first-ever school in the slums. There, the shadow healer meets Roa, a young girl with big dreams of adventure and bold claims of being the daughter of a legendary swordsman—the former Sword Saint.
When Roa runs into trouble, she finds herself face-to-face with the current Sword Saint and resolves to become the woman’s apprentice. Between this fateful meeting and a little push from a certain meddling wraith, Zenos finds himself dragged back into the adventuring lifestyle for the first time in a long while...