Goblin Slayer Side Story: Year One, Vol. 2 (light novel‪)‬

The die is cast.
During one of his usual raids, the young man who has come to be known as Goblin Slayer discovers a ring that glows with a mysterious, fiery light. In his quest to identify it, he's introduced to Arc Mage, an eccentric wizard who lives on the edge of town. She enlists Goblin Slayer's help in revising the Monster Manual, a task the Guild has entrusted to her. It just so happens that the article she's been assigned to write is about...goblins.
Arc Mage and the young Goblin Slayer's ongoing research takes them to the ends of the earth, where they eventually reach an ominous, dark tower...It'll take some teamwork to get all the way to the top!