Frieren: Beyond Journey's End. Volume 12: Kanehito Yamada

The adventure is over but life goes on for an elf mage just beginning to learn what living is all about.
Elf mage Frieren and her courageous fellow adventurers have defeated the Demon King and brought peace to the land. But Frieren will long outlive the rest of her former party. How will she come to understand what life means to the people around her?
Upon touching the ancient monument of the Goddess, Frieren finds herself cast back in time to 53 years before the death of Himmel the Hero. Her old adventuring comrades don’t know she has come from the future, and Frieren realizes she must protect the secrecy of advancements in magic from their enemies. Here, the Demon King has not yet been defeated, and his minions are still powerful and determined to destroy Frieren!