Am I Actually the Strongest?

I, a Hikikomori, was suddenly reincarnated into a prince in a different realm, but because of my weak magical abilities, I was doomed to die on my very first day of existence. I came upon a huge creature right when I thought I was alone in the far-off forest. I attempted to use magic to fight the monster in order to defend myself, but for some reason, the monster changed into a gorgeous female and even became my servant! In a daze, I became a "Devil King" and began a new harem life!