I think eton is reton (the brother) because:
1: I'm sure he called rize 'mother' or she called him 'son' (or maybe they just look similar)
2: he said he had different hair colour
3: he said he would burn every family member except for them two(remember he will probably hate his mother)
4: hence the burning, he seems a lot like the curse
5: their names are similar, and he said he was stripped of his name
6: the ancient language is difficult to know, and both of them know it
7: We already know how time travel is possible (mc) perhaps Rayton traveled back twice, first time was a fail and the second time he also got a second body and studied magic in secret to prevent something from happening
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