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

MIRA’S BOUND FOR VALHALLA!
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… Series Overview: Sakamori Kagami was one of the top players in the VRMMO Ark Earth Online as Danblf, a veteran summoner with the gravitas to match his elite status.
When he falls asleep playing one day, he’s transported to a world where the game is reality—but instead of his all-powerful avatar, he’s stuck in the body of a cute young girl! He can’t let anyone know that this little cutie is really Danblf, so he takes the name “Mira” and claims to be Danblf’s disciple. If this gets out, he’ll never live it down!