Ayakami Shizume ~Shoujo no Ketsudan, Miko no Ketsui~

Midori spots her boyfriend with another woman at the station and follows them to the mountain where she gets lost. Unable to find her partner or the way back, she witnesses an unbelievable scene.

A strange humanoid figure is fighting a lizard monster that is much larger than a normal animal. The unfamiliar person wins, and Midori shuts her eyes tight, thinking that she is going to become the next target. But when she looks in front of her again, she sees a naked woman, the same one that was with her boyfriend earlier.

[Translated from Getchu]