Disclaimer: I dont own Cave Story, or the characters. But I did write the story.
Quote's feelings based on the "Bad Ending" Semi Spoiler-y. Enjoy.
For the longest time I felt things that humans felt. As I blasted my way through cave after cave I felt tired. I swear I could feel my lungs scream for air, muscles that I never possessed burned. I had thoughts and emotions. And when they told me I was a robot, I was surprised.
Then at that moment, as I stared hard at Kazumas expression while he stood there waiting, I was faced with the most human of decisions I would ever have to make. Did I abandon the Mimigas and eventually, the humans as well? Or did I remain, seek out the doctor, and destroy him once and for all? I weighed the options much as any human would. I pondered my choices, and the consequences they would bring.
The realization I would make would have my very human heart breaking. I was a machine. And as a machine I had my limits. The human feeling of hopelessness overcame me.
"No one would blame you. We can't expect you to bear the weight of the world on your shoulders."
I looked at him sadly. But in the end I knew he was right. I was one robot. I wasn't human, no matter how many human thoughts and feelings I had.
I made my choice. Climbing on top of his dragon, with Kazuma behind me, I looked over my shoulder as we took to the skies and watched the island I was abandoning grow farther and farther away. A sinking feeling formed in my chest and I assumed it was guilt. I was much more aware of my robotic existence now.
I counted the days that passed since Kazuma and I came to habituate on our spot hidden in some secret mountains down on the surface world. It was 207 days since we left. I was certain everyone I had come to meet and know was long gone. It made me sad.
Kazuma keeps telling me it's not my fault, and that it was inevitable. The Doctor would have found a way to win one way or another. As he said before, it was inevitable the moment he got his hands on that crown.
Today I languish in my sadness. I regret my decision. The island above has an evil looking red aura surrounding it, and no matter what Kazuma says, it's all my fault. I battle with myself, whether or not I'm more human or robot. In the end I decide that I'm human after all. Robots are supposed to be efficient, perfectly processing systems, and yet here I was 207 days later, 207 days after I made the wrong choice. Only humans make wrong choices.