one with the Core

Sabre never knew his past, all he knew was that he exsisted and he never questioned it even when people would look at him Strangely when he mentioned not knowing his childhood or anything from before he came into this world. So when he runs away with Light after taking the rainbow crystal to keep it safe from the Corrected sun he starts to think more about it, how did he know so much and yet not know how he knew it?
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and why couldn't he control the red lightning that randomly appeared over his body?