After completing 21. The Gladius side quest in Trinity Trigger, speak with Glaive again to obtain the 22. The Bowsong side quest. For this quest, you’ll need to travel to the Bowsong in Astrum and teleport to the end of the dungeon.
Once there, you’ll find that a new path has opened. Make your way through this area until you reach the altar. Once you’ve acquired a bow for Zantis, return to Glaive to complete the quest. As a reward, you’ll receive a Skill Booster IV, Quality Moonstone x4 and Quality Taaffeite x4.