I Surrendered My Sword for a New Life as a Mage: Volume 2 by Shin Kouduki

Soma, Aina, and Lina have begun their journey in search of a way to use magic. With no leads and no other means of making money, the three decide to register as adventurers at a guild. There they meet the mysterious Sierra, who tells them of ancient ruins where a mystical power lies dormant. Soma can’t pass up the chance that whatever it is might grant him the ability to use magic, but traversing the ruins will pit them against forces they don’t understand.