Amatsuki

Ordinary high school student, Tokidoki Rikugō, has to take supplementary History classes, to boost his failing grade, at a state-of-the-art museum. This museum allows the visitor to use high-tech virtual reality to reconstruct a realistic Edo of the Bakumatsu period. However, once the simulation begins, Tokidoki is attacked by a strange creature. After something happens to his left eye, he realizes that he is not wearing the VR goggles - it is no longer a simulation; he's trapped in the virtual world and has no way of getting back.

Synopsis from Anime News Network