Available in the Adventurer's guild after completing Spider Infestation.
The main difficulty of the quest comes from the mature spiders. On turn 3, they use their web skill to debuff Aura's DEF and AGI, making her take far more damage. Having 12 ATK allows to reliably kill those enemies in two strikes.
Alternatively, knowing Light or Fire allows to set up tactical advantage to one-shot the mature spiders with 9 ATK.
Bombs can also one-shot the mature spiders and set up tactical advantage, making even a weak Aura able to deal with the encounter involving two mature spiders.
After clearing the enemies and examining the chasm, just report to the guild to complete the quest.