Tegami Bachi: Letter Bee

Lag, as well as Niche and Steak, a strange animal that tags along with Niche, reaches the town of Kyrie where the bridge Bifrost connects to Yuusari. There they meet Nelli, who guides them to an inn to stay the night, and volunteers to take Lag's bag up to his room, but then suddenly disappears. Nelli's aim is actually to get Lag's crossing pass into Yuusari.