The Rising of the Shield Hero Volume 06 by Aneko Yusagi

After their battle with Glass, Naofumi and the other heroes have a meeting with the queen and Naofumi is shocked to learn about the seven star heroes. Still reeling from this revelation, more drama unfolds on the islands before Naofumi and his party can return to Melromarc. He meets Rishia, who is betrayed by Itsuki and his party members. Naofumi sympathizes with her and invites her to join his party. Eventually, Naofumi discovers that she has a talent for magic, but before they can develop her powers, they are needed elsewhere. A massive monster bearing the appearance of a giant tortoise must be defeated. The monster is so powerful that even the mightiest adventurers cannot defeat him–so what hope is there for Naofumi?