Is It Wrong to Try to Pick Up Girls in a Dungeon?, Vol. 5 (manga) — Fujino Omori

In pursuit of his desire to become stronger, the adventurer Bell Cranell has become the student of the brilliant swordswoman Aiz Wallenstein. Even as he despairs at the vast gulf between his abilities and hers, he begins to improve. As he does so, though, a certain goddess's shadowy plan steadily advances, and with it, a dark shadow approaches. The familia myth--walked by the boy and written by the goddess--continues!