Hazure Skill: The Guild Member with a Worthless Skill Is Actually a Legendary Assassin, Vol. 7 (light novel) — Kennoji

HAUNTED BY PAST SINS…
Rila never wanted to start a war with humanity. Yet it happened nonetheless, and the destruction still weighs on her conscience. While she longs for a way to make amends, a mysterious figure contacts her, offering the former demon lord redemption and then spiriting her away. Naturally, Roland and the others refuse to let anyone take Rila and set out to find her. Their search points them to Yorvensen, a country ruined by the Human-Fiend War. Supposedly, the dead have returned to rebuild the nation...