Goblin Slayer Side Story: Year One, Vol. 4 (light novel) — Kumo Kagyu

While Goblin Slayer is off hunting goblins, he encounters a mysterious elf fighter. For her own reasons, this blue-haired woman decides to join him on his hunts, and they work together. The payment? Training in the sword from this elf fighter. A standard adventure ends, giving way to days of hard training. When Goblin Slayer and his new acquaintance head for a cave that other adventurers have entered never to return, Chaos is waiting for them...