Ancient God

An ancient battle was so shocking that the sky was broken into six parts.
Countless years later, a generation of young boy Xuantian was born in the lowest level of heaven and earth holding a weapon fragment. He was born with a disability, suffered from headaches, and had a very weird brain.
Finally one day, the abnormality in my mind became clear. It turned out to be memory fragments, recording a corner of Ancient Times.
Oh my God! It turned out to be a scene of fighting on an ancient battlefield, with all races stained with blood and beasts roaring, earth-shaking.
Who am I? Why is there a lack of memory?