Situation puzzleThe black bird

I was alone in the mountains studying birds. When I accidentally fell from a height and broke my leg, I noticed an unknown black bird. I couldn't even get up, and I would have died of thirst or hunger if it hadn’t been for a strange girl who started coming to me every night. She had black hair, long eyelashes, and a charming smile. She never talked but just lay on top of me and fed me from her mouth. I thought it was raw meat. Sometimes, she gave me warm blood to drink, but I was so hungry that enjoyed any food. She left immediately afterwards.

About a month later, my leg felt better. I managed to get up, return home, and finally have a proper meal. I was surprised when at night she somehow got into my room again and woke me up. Chewing something, she slowly started climbing on top of me again. I tried to resist, but in vain. She forced the food into my mouth and left, smiling. This time I was full, so I felt an aversion. Spitting everything out on the floor and recollecting myself, I managed see pieces of someone’s eye in this lump.

Since then, it happened every night. Although I was grateful to her for saving me, I begin to feel really worried. Fortunately, she stopped visiting me after a couple of weeks.

Five years have passed since then. I’m on Mount Fuji now, and here I met the black bird again. Now I understand everything. My time is short. Do you know why?