She Professed Herself Pupil of the Wise Man (Light Novel) Vol. 16

Strange amulets are popping up, their origins seemingly demonic, and Mira's determined to figure out more about them. Yet tampering with the amulets is risky not just to Mira but also to her environment. She needs to sate her curiosity in a location that's impervious to the damage the amulets may potentially cause--and she suspects the Valkyries' stomping grounds, Valhalla, could be perfect! Still, even heading to Valhalla might not stop the amulets' infernal source from getting the upper hand over Mira herself...